Method for discovering device in wireless communication system supporting device-to-device communication and apparatus for same

ABSTRACT

Disclosed are a terminal discovery method in a wireless communication system supporting device-to-device (D2D) communication, and a device therefor. The method for discovering a terminal in a wireless communication system supporting device-to-device (D2D) communication, includes transmitting, by a terminal, a discovery signal, and receiving, by the terminal, a response signal as a response with respect to the discovery signal from a different terminal, wherein the response signal is transmitted by the different terminal when a response delay time determined on the basis of a reception signal-to-interference noise ratio (SINR) terminates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/002086, filed on Mar. 4, 2015,which claims the benefit of U.S. Provisional Application Nos.61/947,975, filed on Mar. 4, 2014, and 62/056,622, filed on Sep. 29,2014, the contents of which are all hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a response delay-based terminal discovery methodin a wireless communication system supporting device-to-device (D2D)communication, and a device supporting the same

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

In the present invention, in a state in which the entirety or a portionof a communication infrastructure may not be used in a disastersituation, terminals in a disaster area may attempt at searching for aneighbor base station and accessing or a terminal not able to search fora neighbor base station may be connected to an infrastructure networkthrough hopping using a relay function of a neighbor terminal. Here,indiscriminate signal transmissions may be made, leading to resourceconflict between D2D terminals or between cellular resources and anineffective use of resource.

Therefore, an object of the present invention is to provide a method foreffectively searching for a neighbor terminal on the basis of responsedelay, while minimizing resource conflict.

Technical subjects of the present invention that may be obtained in thepresent invention are not limited to the foregoing technical subjectsand any other technical subjects not mentioned herein may be easilyunderstood by a person skilled in the art from the present disclosureand accompanying drawings.

Technical Solution

According to an aspect of the present invention, there is provided amethod for discovering a terminal in a wireless communication systemsupporting device-to-device (D2D) communication, including:transmitting, by a terminal, a discovery signal; and receiving, by theterminal, a response signal as a response with respect to the discoverysignal from a different terminal, wherein the response signal istransmitted by the different terminal when a response delay timedetermined on the basis of a reception signal-to-interference noiseratio (SINR) terminates.

According to another aspect of the present invention, there is provideda terminal for discovering a terminal in a wireless communication systemsupporting device-to-device (D2D) communication, including: a radiofrequency (RF) unit transmitting and receiving a wireless signal; and aprocessor, wherein the processor is configured to transmit a discoverysignal and receive a response signal as a response with respect to thediscovery signal from a different terminal, and the response signal istransmitted by the different terminal when a response delay timedetermined on the basis of a reception signal-to-interference noiseratio (SINR) terminates.

Preferably, the response delay time may be determined to be in inverseproportion to the reception SINR.

Preferably, the method may further include: selecting, by the terminal,a terminal for performing a terminal discovery process at a nextdiscovery period, from among terminals which have transmitted theresponse signal; and transmitting, by the terminal, information of aresource pool for transmission of a discovery message to the selectedterminal.

Preferably, the terminal for performing the terminal discovery processat the next discovery period may be selected as a terminal which hasfirst transmitted the response signal.

Preferably, the terminal for performing the terminal discovery processat the next discovery period may be selected as a terminal which hastransmitted the response signal the latest.

Preferably, the terminal for performing the terminal discovery processat the next discovery period may be selected randomly.

Preferably, the discovery signal may include a terminal identifierand/or discovery period information.

Preferably, the method may further include: after transmitting thediscovery signal, switching the terminal to a reception mode.

According to another aspect of the present invention, there is provideda method for discovering a terminal in a wireless communication systemsupporting device-to-device (D2D) communication, including: receiving,by a terminal, a discovery signal; determining, by the terminal, aresponse delay time on the basis of a reception signal-to-interferencenoise ratio (SINR); and transmitting, by the terminal, a response signalas a response with respect to the discovery signal when the responsedelay time terminates.

According to another aspect of the present invention, there is provideda terminal for discovering a terminal in a wireless communication systemsupporting device-to-device (D2D) communication, including: a radiofrequency (RF) unit transmitting and receiving a wireless signal; and aprocessor, wherein the processor is configured to receive a discoverysignal, determine a response delay time on the basis of a receptionsignal-to-interference noise ratio (SINR), and transmit a responsesignal as a response with respect to the discovery signal when theresponse delay time terminates.

Preferably, the response delay time may be determined to be in inverseproportion to the reception SINR.

Preferably, the reception SINR may be derived on the basis of thediscovery signal or a reference signal transmitted from the terminalwhich has transmitted the discovery signal.

Advantageous Effects

According to embodiments of the present invention, since a D2D signal istransmitted on the basis of response delay in a wireless communicationsystem supporting D2D communication, a neighbor terminal may beeffectively searched, while minimizing resource conflict between D2Dterminals or between cellular resources.

Advantages and effects of the present invention that may be obtained inthe present invention are not limited to the foregoing effects and anyother technical effects not mentioned herein may be easily understood bya person skilled in the art from the present disclosure and accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The above and/or other aspects of the present invention will be moreapparent by describing certain exemplary embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a view illustrating a structure of a wireless frame in awireless communication system to which the present invention may beapplied.

FIG. 2 is a view illustrating a resource grid of a downlink slot in awireless communication system to which the present invention may beapplied.

FIG. 3 is a view illustrating a structure of a downlink subframe in awireless communication system to which the present invention may beapplied.

FIG. 4 is a view illustrating a structure of an uplink subframe in awireless communication system to which the present invention may beapplied.

FIG. 5 is a view illustrating an example in which PUCCH formats aremapped to PUCCH regions of uplink physical resource blocks in a wirelesscommunication system to which the present invention may be applied.

FIG. 6 is a view illustrating a structure of a CQI channel in case of ageneral CP in a wireless communication system to which the presentinvention may be applied.

FIG. 7 is a view illustrating a structure of an ACK/NACK channel in caseof general CP in a wireless communication system to which the presentinvention may be applied.

FIG. 8 is a view illustrating an example in which five SC-FDMA symbolsare generated and transmitted during a single symbol in a wirelesscommunication system to which the present invention may be applied.

FIG. 9 is a view illustrating an example in which a component carrierand a carrier are merged in a wireless communication system to which thepresent invention may be applied.

FIG. 10 is a view illustrating an example of a structure of a subframein accordance with cross carrier scheduling in a wireless communicationsystem to which the present invention may be applied.

FIG. 11 is a view illustrating an example of processing a transportchannel of a UL-SCH in a wireless communication system to which thepresent invention may be applied.

FIG. 12 is a view illustrating an example of processing a signal of anuplink shared channel, a transport channel, in a wireless communicationsystem to which the present invention may be applied.

FIG. 13 is a view illustrating a configuration of a general multi-inputmulti-output (MIMO) communication system.

FIG. 14 is a view illustrating a channel from a plurality oftransmission antennas to a single reception antenna.

FIG. 15 is a view illustrating a pattern of reference signals mapped todownlink resource block pairs in a wireless communication system towhich the present invention may be applied.

FIG. 16 is a view illustrating an uplink subframe including a soundingreference signal symbol in a wireless communication system to which thepresent invention may be applied.

FIG. 17 is a view illustrating dividing resource of a relay node in awireless communication system to which the present invention may beapplied.

FIG. 18 is a view conceptually illustrating D2D communication in awireless communication system to which the present invention may beapplied.

FIG. 19 is a view illustrating examples of various scenarios of D2Dcommunication to which a method proposed in the present disclosure isapplicable.

FIG. 20 is a view illustrating an example of allocating discoveryresource according to an embodiment of the present invention.

FIG. 21 is a view briefly illustrating a discovery process according toan embodiment of the present invention.

FIG. 22 is a view illustrating terminals receiving a reference signalaccording to an embodiment of the present invention.

FIG. 23 is a view illustrating a method for transmitting a D2D discoverymessage according to an embodiment of the present invention.

FIG. 24 is a view illustrating an example of dividing and settingdiscovery resource regions according to an embodiment of the presentinvention.

FIG. 25 is a view illustrating an example of dividing and settingdiscovery resource regions according to an embodiment of the presentinvention.

FIG. 26 is a view illustrating an example of dividing and settingdiscovery resource regions according to an embodiment of the presentinvention.

FIG. 27 is a view illustrating a scheme of determining discoveryresource regions on the basis of a signal transmitted from a UEaccording to an embodiment of the present invention.

FIG. 28 is a view illustrating a situation in which UEs in a disasterarea access an infrastructure network according to an embodiment of thepresent invention.

FIG. 29 is a view illustrating a UE discovery method according to anembodiment of the present invention.

FIG. 30 is a view illustrating a D2D UE discovery method according to anembodiment of the present invention.

FIG. 31 is a view illustrating a UE discovery method according to anembodiment of the present invention.

FIG. 32 is a view illustrating a UE discovery method according to anembodiment of the present invention.

FIG. 33 is a view illustrating a method for allocating resourcesimultaneously with UE discovery according to an embodiment of thepresent invention.

FIG. 34 is a view illustrating a UE discovery method according to anembodiment of the present invention.

FIG. 35 is a view illustrating a difference between an existing UEdiscovery method and a UE discovery method proposed in the presentinvention.

FIG. 36 is a view illustrating results of a simulation of UE discoveryperformance of response delay-based UE discovery according to anembodiment of the present invention.

FIG. 37 is a view illustrating results of a simulation of infrastructureaccess performance of a response delay-based UE discovery methodaccording to an embodiment of the present invention.

FIG. 38 is a view illustrating a block diagram of a wirelesscommunication device according to an embodiment of the presentinvention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome exemplary embodiments of the present invention and are not intendedto describe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to Which the Present Invention May Be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

FIG. 1(a) illustrates the radio frame structure type 1. A radio frameconsists of 10 subframes. One subframe consists of 2 slots in a timedomain. The time taken to send one subframe is called a TransmissionTime Interval (TTI). For example, one subframe may have a length of 1ms, and one slot may have a length of 0.5 ms.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) illustrates the frame structure type 2. The radio framestructure type 2 consists of 2 half frames. Each of the half framesconsists of 5 subframes, a Downlink Pilot Time Slot (DwPTS), a GuardPeriod (GP), and an Uplink Pilot Time Slot (UpPTS). One subframeconsists of 2 slots. The DwPTS is used for initial cell search,synchronization, or channel estimation in UE. The UpPTS is used forchannel estimation in an eNB and to perform uplink transmissionsynchronization with UE. The guard period is an interval in whichinterference generated in uplink due to the multi-path delay of adownlink signal between uplink and downlink is removed.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes. Table 1 shows theuplink-downlink configuration.

TABLE 1 UL-DL DL-to-UL configure- Switch-point Subframe number tionperiodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S UU D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 410 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U UD S U U D

Referring to Table 1, in each subframe of the radio frame, “D” isindicative of a subframe for downlink transmission, “U” is indicative ofa subframe for uplink transmission, and “S” is indicative of a specialsubframe including three types of a DwPTS, GP, and UpPTS. Anuplink-downlink configuration may be classified into 7 types. Thepositions and/or number of downlink subframes, special subframes, anduplink subframe are different in each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

The structure of a radio frame is only one example. The number ofsubcarriers included in a radio frame or the number of slots included ina subframe and the number of OFDM symbols included in a slot may bechanged in various ways.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs N^(DL) included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain A physical uplink controlchannel (PUCCH) carrying uplink control information is allocated to thecontrol region. A physical uplink shared channel (PUSCH) carrying userdata is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Physical Uplink Control Channel (PUCCH)

The Uplink Control Information (UCI) transmitted through a PUCCH caninclude

Scheduling Request (SR), HARQ ACK/NACK information, and downlink channelmeasurement information as shown below.

-   -   SR (Scheduling Request): used for requesting uplink UL-SCH        resources. SR is transmitted by On-Off Keying (OOK) scheme.    -   HARQ ACK/NACK: a signal responding to a downlink data packet on        a PDSCH. This signal indicates whether a downlink data packet        has successfully received or not. ACK/NACK 1 bit is transmitted        in response to a single downlink codeword while ACK/NACK 2 bits        are transmitted in response to two downlink codewords.    -   CSI (Channel State Information): feedback information about a        downlink channel. CSI can include at least one of a Channel        Quality Indicator (CQI), a Rank Indicator (RI), a Precoding        Matrix Indicator (PMI), and a Precoding Type Indicator (PTI).        For each subframe, 20 bits are used to represent the CSI.

HARQ ACK/NACK information may be generated depending on whether adownlink data packet on a PDSCH has been successfully decoded. In anexisting wireless communication system, 1 bit is transmitted as ACK/NACKinformation with respect to the transmission of downlink singlecodeword, and 2 bits are transmission as ACK/NACK information withrespect to the transmission of downlink 2 codewords.

Channel measurement information denotes feedback information related toa Multiple Input Multiple Output (MIMO) scheme and may include a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI), and a RankIndicator (RI). Such channel measurement information may be commonlycalled a CQI.

In order to transmit a CQI, 20 bits may be used in each subframe.

A PUCCH may be modulated using a Binary Phase Shift Keying (BPSK) schemeand a Quadrature Phase Shift Keying (QPSK) scheme. Control informationfor a plurality of UEs may be transmitted through a PUCCH. If CodeDivision Multiplexing (CDM) is performed in order to distinguish thesignals of UEs from each other, a Constant Amplitude ZeroAutocorrelation (CAZAC) sequence of a length 12 is mostly used. TheCAZAC sequence has a characteristic in that a constant size (amplitude)is maintained in a time domain and a frequency domain. Accordingly, theCAZAC sequence has a property suitable for increasing coverage bylowering the Peak-to-Average Power Ratio (PAPR) or Cubic Metric (CM) ofUE. Furthermore, ACK/NACK information about downlink data transmissiontransmitted through a PUCCH is covered using an orthogonal sequence oran Orthogonal Cover (OC).

Furthermore, control information transmitted through a PUCCH may bedistinguished from each other using a cyclically shifted sequence havinga different Cyclic Shift (CS) value. The cyclically shifted sequence maybe generated by cyclically shifting a base sequence by a specific CSamount. The specific CS amount is indicated by a CS index. The number ofavailable CSs may be different depending on delay spread of a channel Avariety of types of sequences may be used as the base sequence, and theCAZAC sequence is an example of the sequences.

Furthermore, the amount of control information that may be transmittedby UE in one subframe may be determined depending on the number ofSC-FDMA symbols which may be used to send the control information (i.e.,SC-FDMA symbols other than SC-FDMA symbols which are used to send aReference Signal (RS) for the coherent detection of a PUCCH).

In a 3GPP LTE system, a PUCCH is defined as a total of 7 differentformats depending on control information that is transmitted, amodulation scheme, and the amount of control information. The attributesof Uplink Control Information (UCI) transmitted according to each PUCCHformat may be summarized as in Table 2 below.

TABLE 2 PUCCH Format Uplink Control Information (UCI) Format 1Scheduling Request (SR)(unmodulated waveform) Format 1a 1-bit HARQACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACK with/without SRFormat 2 CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK(20 bits) for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK(20 + 1 coded bits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 codedbits) Format 3 HARQ ACK/NACK, SR, CSI (48 coded bits)

The PUCCH format 1 is used for SR-only transmission. In the case ofSR-only transmission, a not-modulated waveform is applied. This isdescribed in detail later.

The PUCCH format 1a or 1b is used to send HARQ ACK/NACK. If HARQACK/NACK is solely transmitted in a specific subframe, the PUCCH format1a or 1b may be used. Alternatively, HARQ ACK/NACK and an SR may betransmitted in the same subframe using the PUCCH format 1a or 1b.

PUCCCH 2 is used for transmission of CQI, and PUCCH format 2a or 2b isused for transmission of CQI and HARQ ACK/NACK. In the case of extendedCP, PUCCH format 2 may be used for transmission of CQI and HARQACK/NACK.

PUCCH format 3 is used for carrying an encoded UCI of 48 bits. PUCCHformat 3can carry HARQ ACK/NACK about a plurality of serving cells, SR(if exists), and a CSI report about one serving cell.

FIG. 5 shows an example of a form in which the PUCCH formats are mappedto the PUCCH region of the uplink physical resource block in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

In FIG. 5, N_(RB) ^(UL) is indicative of the number of RBs in uplink,and 0, 1, . . . , N_(RB) ^(UL)−1 means the number of physical RBs.Basically, a PUCCH is mapped to both edges of an uplink frequency block.As shown in FIG. 5, the PUCCH format 2/2a/2b is mapped to a PUCCH regionindicated by m=0, 1. This may represent that the PUCCH format 2/2a/2b ismapped to RBs located at a band edge. Furthermore, the PUCCH format2/2a/2b and the PUCCH format 1/1a/1b may be mixed and mapped to a PUCCHregion indicated by m=2. Furthermore, the PUCCH format 1/1a/1b may bemapped to a PUCCH region indicated by m=3, 4, 5. UEs within a cell maybe notified of the number N_(RB) ⁽²⁾ of PUCCH RBs which may be used bythe PUCCH format 2/2a/2b through broadcasting signaling.

The PUCCH format 2/2a/2b is described below. The PUCCH format 2/2a/2b isa control channel for transmitting channel measurement feedback (i.e., aCQI, a PMI, and an RI).

The report cycle of channel measurement feedback (hereinafter commonlycalled “CQI information”) and a frequency unit (or frequency resolution)to be measured may be controlled by an eNB. In a time domain, a periodicor aperiodic CQI report may be supported. The PUCCH format 2 may be usedfor a periodic report, and a PUSCH may be used for an aperiodic report.In the case of an aperiodic report, an eNB may instruct UE to carry anindividual CQI report on a resource scheduled to transmit uplink data.

FIG. 6 shows the structure of a CQI channel in the case of a normal CPin a wireless communication system to which an embodiment of the presentinvention may be applied.

The SC-FDMA symbols 1 and 5 (i.e., the second and the sixth symbols) ofthe SC-FDMA symbols 0 to 6 of one slot are used to transmit ademodulation reference signal (DMRS), and the remaining SC-FDMA symbolsof the SC-FDMA symbols 0 to 6 of the slot may be used to CQIinformation. Meanwhile, in the case of an extended CP, one SC-FDMAsymbol (SC-FDMA symbol 3) is used for DMRS transmission.

In the PUCCH format 2/2a/2b, modulation by a CAZAC sequence issupported, and a QPSK-modulated symbol is multiplied by a CAZAC sequenceof a length 12. A Cyclic Shift (CS) of the sequence is changed between asymbol and a slot. Orthogonal covering is used for a DMRS.

A reference signal (DMRS) is carried on 2 SC-FDMA symbols that belong to7 SC-FDMA symbols included in one slot and that is spaced at 3 SC-FDMAsymbols. CQI information is carried on the remaining 5 SC-FDMA symbolsof the 7 SC-FDMA symbols. Two RSs are used in one slot in order tosupport high-speed UE. Furthermore, UEs are distinguished from eachother using Cyclic Shift (CS) sequences. CQI information symbols aremodulated into all SC-FDMA symbols and transferred. The SC-FDMA symbolsconsist of one sequence. That is, UE modulates a CQI using each sequenceand sends the CQI.

The number of symbols which may be transmitted in one TTI is 10, and themodulation of CQI information is determined up to QPSK. If QPSK mappingis used for an SC-FDMA symbol, a CQI value of 10 bits may be carried onone slot because a CQI value of 2 bits may be carried on the SC-FDMAsymbol. Accordingly, a CQI value having a maximum of 20 bits may becarried on one subframe. Frequency domain spread code is used to spreadCQI information in a frequency domain.

A CAZAC sequence (e.g., ZC sequence) of a length 12 may be used as thefrequency domain spread code. Control channels may be distinguished fromeach other by applying CAZAC sequences having different cyclic shiftvalues. IFFT is performed on frequency domain-spread CQI information.

12 different UEs may be subjected to orthogonal multiplexing on the samePUCCH RB by 12 cyclic shifts having the same interval. In the case of anormal CP, a DMRS sequence on the SC-FDMA symbols 1 and 5 (on an SC-FDMAsymbol 3 in the case of an extended CP) are similar to a CQI signalsequence on a frequency domain, but modulation, such as CQI information,is not applied to the DMRS sequence.

UE may be semi-statically configured by higher layer signaling so thatit periodically reports different CQI, PMI and RI Types on PUCCHresources indicated by PUCCH resource indices n_(PUCCH)^((1,{tilde over (p)})), n_(PUCCH) ^((2,{tilde over (p)})), andn_(PUCCH) ^((3,{tilde over (p)})). In this case, the PUCCH resourceindex n_(PUCCH) ^((2,{tilde over (p)})) is information indicative of aPUCCH region that is used to transmit the PUCCH format 2/2a/2b and thevalue of a Cyclic Shift (CS) to be used.

Hereinafter, the PUCCH format 1a and 1b is described below.

In the PUCCH format 1a/1b, a symbol modulated using a BPSK or QPSKmodulation scheme is multiplied by a CAZAC sequence of a length 12. Forexample, the results of a modulation symbol d(0) by a CAZAC sequencer(n)(n=0, 1, 2, . . . , N−1) of a length N become y(0), y(1), y(2), . .. , y(N−1). The symbols y(0), . . . , y(N−1) may be called a block ofsymbols. After the modulation symbol is multiplied by the CAZACsequence, block-wise spread using an orthogonal sequence is applied.

A Hadamard sequence of a length 4 is used for common ACK/NACKinformation, and a Discrete Fourier Transform (DFT) sequence of a length3 is used for shortened ACK/NACK information and a reference signal.

In the case of an extended CP, a Hadamard sequence of a length 2 is usedin a reference signal.

FIG. 7 shows the structure of an ACK/NACK channel in the case of anormal CP in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 7 illustrates a PUCCH channel structure for transmitting HARQACK/NACK without a CQI.

A Reference Signal (RS) is carried on 3 contiguous SC-FDMA symbol thatbelong to 7 SC-FDMA symbols included in one slot and that are placed ina middle portion, and an ACK/NACK signal is carried on the remaining 4SC-FDMA symbols of the 7 SC-FDMA symbols.

Meanwhile, in the case of an extended CP, an RS may be carried on 2contiguous symbols placed in the middle of one slot. The number andpositions of symbols used in an RS may be different depending on controlchannels, and the number and positions of symbols used in an ACK/NACKsignal associated with the control channels may be changed depending onthe number and positions of symbols used in the RS.

ACK information (not-scrambled state) of 1 bit and 2 bits may berepresented as one HARQ ACK/NACK modulation symbol using respective BPSKand QPSK modulation schemes. Positive ACK (ACK) may be encoded as “1”,and negative ACK (NACK) may be encoded as “0”.

When a control signal is to be transmitted within an allocatedbandwidth, two-dimensional spreading is applied in order to increasemultiplexing capacity. That is, in order to increase the number of UEsor the number of control channels that may be multiplexed, frequencydomain spreading and time domain spreading are used at the same time.

In order to spread an ACK/NACK signal in a frequency domain, a frequencydomain sequence is used as a base sequence. A Zadoff-Chu (ZC) sequencewhich is one of CAZAC sequences, may be used as the frequency domainsequence. For example, by applying a different Cyclic Shift (CS) to a ZCsequence which is a base sequence, different UEs or different controlchannels may be multiplexed. The number of CS resources supported in aSC-FDMA symbol for PUCCH RBs for transmitting HARQ ACK/NACK isconfigured by a cell-specific upper layer signaling parameter Δ_(shift)^(PUCCH).

An ACK/NACK signal spread in a frequency domain is spread in a timedomain using orthogonal spreading code. A Walsh-Hadamard sequence or DFTsequence may be used as the orthogonal spreading code. For example, anACK/NACK signal may be spread for 4 symbols using an orthogonal sequencew0, w1, w2, or w3 of a length 4. Furthermore, an RS is also spread usingan orthogonal sequence of a length 3 or length 2. This is calledOrthogonal Covering (OC).

A plurality of UEs may be multiplexed using a Code Division Multiplexing(CDM) method using CS resources in a frequency domain and OC resourcesin a time domain, such as those described above. That is, ACK/NACKinformation and RSs of a large number of UEs may be multiplexed on thesame PUCCH RB.

The number of spreading code supported for ACK/NACK information isrestricted by the number of RS symbols with respect to such time domainspreading CDM. That is, the multiplexing capacity of an RS is smallerthan the multiplexing capacity of ACK/NACK information because thenumber of SC-FDMA symbols for RS transmission is smaller than the numberof SC-FDMA symbols for ACK/NACK information transmission.

For example, in the case of a normal CP, ACK/NACK information may betransmitted in 4 symbols. 3 pieces of orthogonal spreading code not 4are used for ACK/NACK information. The reason for this is that only 3pieces of orthogonal spreading code may be used for an RS because thenumber of symbols for RS transmission is limited to 3.

In case that 3 symbols of one slot may be used for RS transmission and 4symbols of the slot may be used for ACK/NACK information transmission ina subframe of a normal CP, for example, if 6 Cyclic Shifts (CSs) may beused in a frequency domain and 3 Orthogonal Cover (OC) resources may beused in a time domain, HARQ ACK from a total of 18 different UEs may bemultiplexed within one PUCCH RB. In case that 2 symbols of one slot areused for RS transmission and 4 symbols of one slot are used for ACK/NACKinformation transmission in a subframe of an extended CP, for example,if 6 CSs may be used in a frequency domain and 2 OC resources may beused in a time domain, HARQ ACK from a total of 12 different UEs may bemultiplexed within one PUCCH RB.

The PUCCH format 1 is described below. A Scheduling Request (SR) istransmitted in such a way as to make a request or does not make arequest that UE is scheduled. An SR channel reuses an ACK/NACK channelstructure in the PUCCH format 1a/1b and consists of an On-Off Keying(OKK) method based on an ACK/NACK channel design. An RS is nottransmitted in the SR channel Accordingly, a sequence of a length 7 isused in the case of a normal CP, and a sequence of a length 6 is used inthe case of an extended CP. Different cyclic shifts or orthogonal coversmay be allocated to an SR and ACK/NACK. That is, in order to send apositive SR, UE sends HARQ ACK/NACK through a resource allocated for theSR. In order to send a negative SR, UE sends HARQ ACK/NACK through aresource allocated for ACK/NACK.

An enhanced-PUCCH (e-PUCCH) format is described below. An e-PUCCH maycorrespond to the PUCCH format 3 of an LTE-A system. A block spreadingscheme may be applied to ACK/NACK transmission using the PUCCH format 3.

Unlike in the existing PUCCH format 1 series or 2 series, the blockspreading scheme is a method of modulating control signal transmissionusing an SC-FDMA method. As shown in FIG. 8, a symbol sequence may bespread in a time domain using Orthogonal Cover Code (OCC) andtransmitted. By using OCC, the control signals of a plurality of UEs maybe multiplexed on the same RB. In the case of the PUCCH format 2, onesymbol sequence is transmitted in a time domain, and the control signalsof a plurality of UEs are multiplexed using a Cyclic Shift (CS) of aCAZAC sequence. In contrast, in the case of a block spreading-basedPUCCH format (e.g., the PUCCH format 3), one symbol sequence istransmitted in a frequency domain, and the control signals of aplurality of UEs are multiplexed using time domain spreading using OCC.

FIG. 8 shows an example in which 5 SC-FDMA symbols are generated andtransmitted during one slot in a wireless communication system to whichan embodiment of the present invention may be applied.

FIG. 8 shows an example in which 5 SC-FDMA symbols (i.e., a data part)are generated using OCC of a length=5 (or SF=5) in one symbol sequenceduring 1 slot and transmitted. In this case, 2 RS symbols may be usedduring the 1 slot.

In the example of FIG. 8, the RS symbols may be generated from a CAZACsequence to which a specific CS value has been applied and may betransmitted in a form in which a specific OCC may be applied (ormultiplied) to a plurality of RS symbols. Furthermore, in the example ofFIG. 8, assuming that 12 modulation symbols are used in each OFDM symbol(or SC-FDMA symbol) and each of the modulation symbols is generated byQPSK, a maximum number of bits capable of being transmitted in one slotare 12×2=24 bits. Accordingly, a total number of bits capable of beingtransmitted in 2 slots are 48 bits. As described above, if a PUCCHchannel structure using a block spreading method is used, controlinformation having an extended size compared to the existing PUCCHformat 1 series and 2 series can be transmitted.

General Carrier Aggregation

A communication environment taken into consideration in embodiments ofthe present invention includes a multi-carrier support environment. Thatis, a multi-carrier system or Carrier Aggregation (CA) system that isused in an embodiment of the present invention refers to a system inwhich one or more Component Carriers (CCs) having a smaller bandwidththan a target bandwidth are aggregated and used when the target widebandis configured in order to support a wideband.

In an embodiment of the present invention, a multi-carrier means of anaggregation of carriers (or a carrier aggregation). In this case, anaggregation of carriers means both an aggregation between contiguouscarriers and an aggregation between discontiguous (or non-contiguous)carriers. Furthermore, the number of CCs aggregated between downlink anduplink may be different. A case where the number of downlink CCs(hereinafter called “DL CCs”) and the number of uplink CCs (hereinaftercalled “UL CCs”) are the same is called a symmetric aggregation. A casewhere the number of DL CCs is different from the number of UL CCs iscalled an asymmetric aggregation. Such the term of a carrier aggregationmay be replaced with terms, such as a carrier aggregation, bandwidthaggregation, or spectrum aggregation.

An object of a carrier aggregation configured by aggregating two or morecomponent carriers is to support up to a 100 MHz bandwidth in an LTE-Asystem. When one or more carriers having a smaller bandwidth than atarget bandwidth are aggregated, the bandwidth of the aggregatedcarriers may be restricted to a bandwidth which is used in an existingsystem in order to maintain backward compatibility with an existing IMTsystem. For example, in an existing 3GPP LTE system, {1.4, 3, 5, 10, 15,20} MHz bandwidths may be supported. In a 3GPP LTE-advanced system(i.e., LTE-A), bandwidths greater than the bandwidth 20 MHz may besupported using only the bandwidths for a backward compatibility withexisting systems. Furthermore, in a carrier aggregation system used inan embodiment of the present invention, new bandwidths may be definedregardless of the bandwidths used in the existing systems in order tosupport a carrier aggregation.

An LTE-A system uses the concept of a cell in order to manage radioresources.

The aforementioned carrier aggregation environment may also be called amulti-cell environment. A cell is defined as a combination of a pair ofa downlink resource (DL CC) and an uplink resource (UL CC), but anuplink resource is not an essential element. Accordingly, a cell mayconsist of a downlink resource only or a downlink resource and an uplinkresource. If specific UE has a single configured serving cell, it mayhave 1 DL CC and 1 UL CC. If specific UE has two or more configuredserving cells, it has DL CCs corresponding to the number of cells, andthe number of UL CCs may be the same as or smaller than the number of DLCCs.

In some embodiments, a DL CC and an UL CC may be configured in anopposite way. That is, if specific UE has a plurality of configuredserving cells, a carrier aggregation environment in which the number ofUL CCs is greater than the number of DL CCs may also be supported. Thatis, a carrier aggregation may be understood as being an aggregation oftwo or more cells having different carrier frequency (the centerfrequency of a cell). In this case, the “cell” should be distinguishedfrom a “cell”, that is, a region commonly covered by an eNB.

A cell used in an LTE-A system includes a Primary Cell (PCell) and aSecondary Cell (SCell). A PCell and an SCell may be used as servingcells. In the case of UE which is in an RRC_CONNECTED state, but inwhich a carrier aggregation has not been configured or which does notsupport a carrier aggregation, only one serving cell configured as onlya PCell is present. In contrast, in the case of UE which is in theRRC_CONNECTED state and in which a carrier aggregation has beenconfigured, one or more serving cells may be present. A PCell and one ormore SCells are included in each serving cell.

A serving cell (PCell and SCell) may be configured through an RRCparameter. PhysCellId is the physical layer identifier of a cell and hasan integer value from 0 to 503. SCellIndex is a short identifier whichis used to identify an SCell and has an integer value of 1 to 7.ServCelllndex is a short identifier which is used to identify a servingcell (PCell or SCell) and has an integer value of 0 to 7. The value 0 isapplied to a PCell, and SCellIndex is previously assigned in order toapply it to an SCell. That is, in ServCelllndex, a cell having thesmallest cell ID (or cell index) becomes a PCell.

A PCell means a cell operating on a primary frequency (or primary CC). APCell may be used for UE to perform an initial connection establishmentprocess or a connection re-establishment process and may refer to a cellindicated in a handover process. Furthermore, a PCell means a cell thatbelongs to serving cells configured in a carrier aggregation environmentand that becomes the center of control-related communication. That is,UE may receive a PUCCH allocated only in its PCell and send the PUCCHand may use only the PCell to obtain system information or to change amonitoring procedure. An Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) may change only a PCell for a handover procedure usingthe RRC connection reconfiguration (RRCConnectionReconfiguration)message of a higher layer including mobility control information(mobilityControllnfo) for UE which supports a carrier aggregationenvironment.

An SCell may mean a cell operating on a secondary frequency (orsecondary CC). Only one PCell is allocated to specific UE, and one ormore SCells may be allocated to the specific UE. An SCell may beconfigured after RRC connection is established and may be used toprovide additional radio resources. A PUCCH is not present in theremaining cells, that is, SCells that belong to serving cells configuredin a carrier aggregation environment and that do not include a PCell.When adding an SCell to UE supporting a carrier aggregation environment,an E-UTRAN may provide all types of system information related to theoperation of a related cell in the RRC_CONNECTED state through adedicated signal. A change of system information may be controlled byreleasing and adding a related SCell. In this case, the RRC connectionreconfiguration (RRCConnectionReconfigutaion) message of a higher layermay be used. An E-UTRAN may send dedicated signaling having a differentparameter for each UE instead of broadcasting within a related SCell.

After an initial security activation process is started, an E-UTRAN mayconfigure a network including one or more SCells by adding to a PCellthat is initially configured in a connection establishing process. In acarrier aggregation environment, a PCell and an SCell may operaterespective component carriers. In the following embodiments, a PrimaryComponent Carrier (PCC) may be used as the same meaning as a PCell, anda Secondary Component Carrier (SCC) may be used as the same meaning asan SCell.

FIG. 9 shows an example of component carriers and a carrier aggregationin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 9a shows the structure of a single carrier used in an LTE system. Acomponent carrier includes a DL CC and an UL CC. One component carriermay have a frequency range of 20 MHz.

FIG. 9b shows the structure of a carrier aggregation used in an LTE-Asystem. FIG. 9b shows an example in which 3 component carriers eachhaving a frequency size of 20 MHz have been aggregated. Three DL CCs andthree UL CCs have been illustrated in FIG. 9, but the number of DL CCsand UL CCs is not limited. In the case of a carrier aggregation, UE maymonitor 3 CCs at the same time, may receive downlink signal/data, andmay transmit uplink signal/data.

If N DL CCs are managed in a specific cell, a network may allocate M(M≤N) DL CCs to UE. In this case, the UE may monitor only the M limitedDL CCs and receive a DL signal. Furthermore, a network may give priorityto L (L≤M≤N) DL CCs and allocate major DL CCs to UE. In this case, theUE must monitor the L DL CCs. Such a method may be applied to uplinktransmission in the same manner.

A linkage between a carrier frequency (or DL CC) of a downlink resourceand a carrier frequency (or UL CC) of an uplink resource may beindicated by a higher layer message, such as an RRC message, or systeminformation. For example, a combination of DL resources and UL resourcesmay be configured by a linkage defined by System Information Block Type2(SIB2). Specifically, the linkage may mean a mapping relationshipbetween a DL CC in which a PDCCH carrying an UL grant is transmitted andan UL CC in which the UL grant is used and may mean a mappingrelationship between a DL CC (or UL CC) in which data for an HARQ istransmitted and an UL CC (or DL CC) in which an HARQ ACK/NACK signal istransmitted.

Cross-Carrier Scheduling

In a carrier aggregation system, there are two methods, that is, aself-scheduling method and a cross-carrier scheduling method form thepoint of view of scheduling for a carrier or a serving cell.Cross-carrier scheduling may also be called cross-component carrierscheduling or cross-cell scheduling.

Cross-carrier scheduling means that a PDCCH (DL grant) and a PDSCH aretransmitted in different DL CCs or that a PUSCH transmitted according toa PDCCH (UL grant) transmitted in a DL CC is transmitted through an ULCC different from an UL CC that is linked to the DL CC through which theUL grant has been received.

Whether cross-carrier scheduling will be performed may be activated ordeactivate in a UE-specific way, and each UE may be notified throughhigh layer signaling (e.g., RRC signaling) semi-statically.

If cross-carrier scheduling is activated, there is a need for a CarrierIndicator Field (CIF) providing notification that a PDSCH/PUSCHindicated by a PDCCH is transmitted through which DL/UL CC. For example,a PDCCH may allocate a PDSCH resource or PUSCH resource to any one of aplurality of component carriers using a CIF. That is, if a PDCCH on a DLCC allocates a PDSCH or PUSCH resource to one of multi-aggregated DL/ULCCs, a CIF is configured. In this case, a DCI format of LTE-A Release-8may be extended according to the CIF. In this case, the configured CIFmay be fixed to a 3-bit field, and the position of the configured CIFmay be fixed regardless of the size of the DCI format. Furthermore, aPDCCH structure (resource mapping based on the same coding and the sameCCE) of LTE-A Release-8 may be reused.

In contrast, if a PDCCH on a DL CC allocates a PDSCH resource on thesame DL CC or allocates a PUSCH resource on a single-linked UL CC, a CIFis not configured. In this case, the same PDCCH structure (resourcemapping based on the same coding and the same CCE) and DCI format asthose of LTE-A Release-8 may be used.

If cross-carrier scheduling is possible, UE needs to monitor a PDCCH fora plurality of pieces of DCI in the control region of a monitoring CCbased on a transmission mode and/or bandwidth corresponding to each CC.Accordingly, there is a need for the configuration of a search space andPDCCH monitoring capable of supporting such monitoring.

In a carrier aggregation system, a UE DL CC set is indicative of a setof DL CCs scheduled so that UE receives a PDSCH. A UE UL CC set isindicative of a set of UL CCs scheduled so that UE transmits a PUSCH.Furthermore, a PDCCH monitoring set is indicative of a set of one ormore DL CCs for performing PDCCH monitoring. A PDCCH monitoring set maybe the same as a UE DL CC set or may be a subset of a UE DL CC set. APDCCH monitoring set may include at least one of DL CCs within a UE DLCC set. Alternatively, a PDCCH monitoring set may be separately definedregardless of a UE DL CC set. DL CCs included in a PDCCH monitoring setmay be configured so that self-scheduling for a linked UL CC is alwayspossible. Such a UE DL CC set, UE UL CC set, and PDCCH monitoring setmay be configured in a UE-specific, UE group-specific, or cell-specificway.

If cross-carrier scheduling is deactivated, it means that a PDCCHmonitoring set is always the same as UE DL CC set. In this case, thereis no indication, such as separate signaling for a PDCCH monitoring set.However, if cross-carrier scheduling is activated, a PDCCH monitoringset may be defined in a UE DL CC set. That is, in order to schedule aPDSCH or PUSCH for UE, an eNB transmits a PDCCH through a PDCCHmonitoring set only.

FIG. 10 shows an example of the structure of a subframe according tocross-carrier scheduling in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 10 shows an example in which 3 DL CCs are aggregated in a DLsubframe for LTE-A UE and a DL CC “A” has been configured as a PDCCHmonitoring DL CC. IF a CIF is not used, each DL CC may send a PDCCH forscheduling its PDSCH without a CIF. In contrast, if a CIF is usedthrough higher layer signaling, only the single DL CC “A” may send itsPDSCH or a PDCCH for scheduling a PDSCH of a different CC using the CIF.In this case, the DL CCs “B” and “C” not configured as PDCCH monitoringDL CCs do not send a PDCCH.

ACK/NACK Multiplexing Method

In a situation in which UE has to simultaneously send a plurality ofACK/NACKs corresponding to a plurality of data units received from aneNB, an ACK/NACK multiplexing method based on the selection of a PUCCHresource may be taken into consideration in order to maintain the singlefrequency characteristic of an ACK/NACK signal and to reduce ACK/NACKtransmission power.

The content of ACK/NACK responses for a plurality of data units,together with ACK/NACK multiplexing, is identified by a combination of aPUCCH resource used in actual ACK/NACK transmission and the resource ofQPSK modulation symbols.

For example, if one PUCCH resource sends 4 bits and a maximum of 4 dataunits are transmitted, ACK/NACK results may be identified in an eNB asin Table 3 below.

TABLE 3 HARQ-ACK (0), HARQ-ACK (1), HARQ-ACK (2), b (0), HARQ-ACK (3)n_(PUCCH) ⁽¹⁾ b (1) ACK, ACK, ACK, ACK n_(PUCCH,1) ⁽¹⁾ 1, 1 ACK, ACK,ACK, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTXn_(PUCCH,2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK,DTX, DTX, DTX n_(PUCCH,0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTXn_(PUCCH,1) ⁽¹⁾ 1, 0 ACK, NACK/DTX, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, NACK/DTX, NACK n_(PUCCH,3) ⁽¹⁾ 1, 1 ACK, NACK/DTX,ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACKn_(PUCCH,0) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH,0) ⁽¹⁾1, 1 NACK/DTX, ACK, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX,DTX n_(PUCCH,1) ⁽¹⁾ 0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 1,0 NACK/DTX, ACK, NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACKn_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾0, 0 NACK/DTX, NACK/DTX, NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 0, 0 DTX, DTX,DTX, DTX N/A N/A

In Table 3, HARQ-ACK (i) is indicative of ACK/NACK results for an i-thdata unit. In Table 3, discontinuous transmission (DTX) means that thereis no data unit transmitted for a corresponding HARQ-ACK(i) or that UEdoes not detect a data unit corresponding to the HARQ-ACK(i).

In accordance with Table 3, a maximum of 4 PUCCH resources n_(PUCCH,0)⁽¹⁾, n_(PUCCH,1) ⁽¹⁾, n_(PUCCH,2) ⁽¹⁾ and n_(PUCCH,3) ⁽¹⁾ are present,and b(0), b(1) has 2 bits transmitted using a selected PUCCH.

For example, if UE successfully receives all of the 4 data units, the UEsends 2 bits (1, 1) using the PUCCH resource n_(PUCCH,1) ⁽¹⁾.

If UE fails in decoding in first and third data units and succeed indecoding in second and fourth data units, the UE sends bits (1, 0) usingthe PUCCH resource n_(PUCCH,3) ⁽¹⁾.

In the selection of an ACK/NACK channel, if at least one ACK is present,NACK and DTX are coupled. The reason for this is that all of ACK/NACKstates are unable to be represented using a combination of a reservedPUCCH resource and a QPSK symbol. If ACK is not present, however, DTX isdecoupled from NACK.

In this case, a PUCCH resource linked to a data unit corresponding toone clear NACK may be reserved in order to send a signal for a pluralityof ACKs/NACKs.

Semi-Persistent Scheduling

Semi-Persistent Scheduling (SPS) is a scheduling method for allocatingresources to specific UE so that the resources continue to be maintainedduring a specific time interval.

If a specific amount of data is transmitted during a specific time as ina Voice over Internet Protocol (VoIP), the waste of control informationcan be reduced using the SPS method because the control information doesnot need to be transmitted at each data transmission interval forresource allocation. In a so-called SPS method, a time resource area inwhich resources may be allocated is first allocated to UE.

In this case, in the semi-persistent allocation method, a time resourcearea allocated to specific UE may be configured to have a cycle. Next,the allocation of time-frequency resources is completed by allocating afrequency resource area, if necessary. The allocation of a frequencyresource area as described above may be called so-called activation. Ifthe semi-persistent allocation method is used, resource allocation ismaintained by one signaling during a specific period. Accordingly,signaling overhead can be reduced because resource allocation does notneed to be repeatedly performed.

Thereafter, if resource allocation for the UE is not required, signalingfor releasing the frequency resource allocation may be transmitted froman eNB to the UE. The release of the allocation of a frequency resourcearea as described above may be called deactivation.

In current LTE, for SPS for uplink and/or downlink, first, UE isnotified of that SPS transmission/reception need to be performed in whatsubframes through Radio Resource Control (RRC) signaling. That is, atime resource of time-frequency resources allocated for SPS is firstdesignated through RRC signaling. In order to notify the UE of availablesubframes, for example, the UE may be notified of the cycle and offsetof a subframe. However, the UE does not immediately performtransmission/reception according to SPS although it has received RRCsignaling because only the time resource area is allocated to the UEthrough RRC signaling. The allocation of the time-frequency resources iscompleted by allocating a frequency resource area, if necessary. Theallocation of a frequency resource area as described above may be calledactivation, and the release of the allocation of a frequency resourcearea may be called deactivation.

Accordingly, the UE receives a PDCCH indicative of activation, allocatesa frequency resource based on RB allocation information included in thereceived PDCCH, and starts to perform transmission/reception based on asubframe cycle and offset allocated through RRC signaling by applying amodulation scheme and coding rate according to Modulation and CodingScheme (MCS) information.

Next, when receiving a PDCCH indicative of deactivation from an eNB, theUE stops the transmission/reception. When a PDCCH indicative ofactivation or reactivation is received after the transmission/receptionis stopped, the UE resumes transmission/reception using a subframe cycleand offset allocated through RRC signaling using RBs and an MCSdesignated in the corresponding PDCCH. That is, the allocation of timeresources is performed through RRC signaling, but thetransmission/reception of actual signals may be performed after a PDCCHindicative of the activation and reactivation of SPS is received. Thestop of signal transmission/reception is performed after a PDCCHindicative of the deactivation of SPS is received.

If the following conditions are all satisfied, the UE may validate aPDCCH including an SPS indication. First, CRC parity bits added forPDCCH payload need to be scrambled with an SPS C-RNTI. Second, a NewData Indicator (NDI) field needs to be set to 0. In this case, in thecase of the DCI formats 2, 2A, 2B, and 2C, an NDI field is indicative ofone of activated transport blocks.

Furthermore, the validation of each field used in the DCI format iscompleted when each field is set based on Table 4 and Table 5 below.When such a validation is completed, the UE recognizes the received DCIinformation as being valid SPS activation or deactivation (or release).In contrast, if the validation is not completed, the UE recognizes thatnon-matching CRC is included in a received DCI format.

Table 4 illustrates fields for PDCCH validation indicative of SPSactivation.

TABLE 4 DCI DCI FORMAT DCI FORMAT FORMAT 0 1/1A 2/2A/2B TPC command forset to “00” N/A N/A scheduled PUSCH Cyclic shift DMRS set to “000” N/AN/A MCS and MSB is set N/A N/A redundancy to “0” version HARQ processN/A FDD: set to FDD: set to “000” number “000” TDD: set to “0000” TDD:set to “0000” MCS N/A MSB is set For an enabled to “0” transport block:MSB is set to “0” Redundancy N/A set to “00” For the enabled versiontransport block: set to “00”

Table 5 illustrates fields for PDCCH validation indicative of SPSdeactivation (or release).

TABLE 5 DCI format 0 DCI format 1A TPC command for scheduled set to “00”N/A PUSCH Cyclic shift DMRS set to “000” N/A MCS and redundancy versionset to “11111” N/A Resource block assignment and Set to all “1”s N/Ahopping resource allocation HARQ process number N/A FDD: set to “000”TDD: set to “0000” MCS N/A set to “11111” Redundancy version N/A set to“00” Resource block assignment N/A Set to all “1”s

If a DCI format is indicative of SPS downlink scheduling activation, aTPC command value for a PUCCH field may be used an index indicative of 4PUCCH resource values set by a higher layer.

PUCCH Piggybacking

FIG. 11 shows an example of transport channel processing for an UL-SCHin a wireless communication system to which an embodiment of the presentinvention may be applied.

In a 3GPP LTE system (=E-UTRA, Rel. 8), in the case of UL, in order toefficiently use the power amplifier of UE, a Peak-to-Average Power Ratio(PAPR) characteristic or Cubic Metric (CM) characteristic affectingperformance of the power amplifier are set to maintain good singlecarrier transmission. That is, in the case of PUSCH transmission in anexisting LTE system, the single carrier characteristic of data may bemaintained through DFT-precoding. In the case of PUCCH transmission, asingle carrier characteristic may be maintained by carrying informationon a sequence having a single carrier characteristic and sending theinformation. However, if DFT-precoded data is discontiguously allocatedbased on a frequency axis, or a PUSCH and a PUCCH are transmitted at thesame time, such a single carrier characteristic is not maintained.Accordingly, if PUSCH transmission is to be performed in the samesubframe as that of PUCCH transmission as in FIG. 11, Uplink ControlInformation (UCI) information to be transmitted through a PUCCH istransmitted (piggybacked) along with data through a PUSCH in order tomaintain the single carrier characteristic.

In a subframe in which a PUSCH is transmitted, a method of multiplexingUplink Control Information (UCI) (a CQI/PMI, HARQ-ACK, an RI, etc.) witha PUSCH region is used because existing LTE UE is unable to send a PUCCHand a PUSCH at the same time as described above.

For example, if a Channel Quality Indicator (CQI) and/or a PrecodingMatrix Indicator (PMI) are to be transmitted in a subframe allocated tosend a PUSCH, UL-SCH data and the CQI/PMI may be multiplexed prior toDFT-spreading and may be transmitted along with control information anddata. In this case, the UL-SCH data is subjected to rate matching bytaking the CQI/PMI resources into consideration. Furthermore, a methodof puncturing the UL-SCH data into control information, such as HARQACK, and an RI, and multiplexing the results with a PUSCH region isused.

FIG. 12 shows an example of a signal processing process in an uplinkshared channel, that is, a transport channel, in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Hereinafter, a signal processing process for an uplink shared channel(hereinafter called an “UL-SCH”) may be applied to one or more transportchannels or control information types.

Referring to FIG. 12, an UL-SCH transfers data to a coding unit in theform of a Transport Block (TB) once for each Transmission Time Interval(TTI).

CRC parity bits p₀, p₁, p₂, p₃, . . . , p_(L-1) are attached to the bitsa₀, a₁, a₂, a₃, . . . , a_(A-1) of the transport block received from ahigher layer at step S120. In this case, A is the size of the transportblock, and L is the number of parity bits. The input bits to which theCRC parity bits have been attached are b₀, b₁, b₂, b₃, . . . , b_(B-1).In this case, B is indicative of the number of bits of the transportblock including the CRC parity bits.

The input bits b₀, b₁, b₂, b₃, . . . , b_(B-1) are segmented intoseveral Code Blocks (CBs) based on the TB size. A CRC is attached to thesegmented several CBs at step S121. Bits after the segmentation of theCBs and the attachment of the CRC are c_(r0), c_(r1), c_(r2), c_(r3), .. . , c_(r(K) _(r) ₋₁₎. In this case, r is a CB number (r=0, . . . ,C−1), and K_(r) is the number of bits according to a CB r. Furthermore,C is a total number of CBs.

Next, channel coding is performed at step S122. Output bits after thechannel coding are d_(r0) ^((i)), d_(r1) ^((i)), d_(r2) ^((i)), d_(r3)^((i)), . . . , d_(r(D) _(r) ₋₁₎ ^((i)). In this case, i is a codedstream index and may have a value 0, 1, or 2 value. D_(r) is the numberof bits of the i-th-coded stream for the CB r. r is a CB number (r=0, .. . , C−1), and C a total number of CBs. Each CB may be coded by turbocoding.

Next, rate matching is performed at step S123. Bits after the ratematching are e_(r0), e_(r1), e_(r2), e_(r3), . . . , e_(r(E) _(r) ₋₁₎.In this case, r is a CB number (r=0, . . . , C−1), and C is a totalnumber of CBs. E_(r) is the number of bits of a r-th code block that hasbeen subjected to rate matching.

Next, a concatenation between the CBs is performed again at step S124.Bits after the concatenation of the CBs are f₀, f₁, f₂, f₃, . . . ,f_(G-1). In this case, G is a total number of coded bits fortransmission. When control information is multiplexed with UL-SCHtransmission, the number of bits used for control informationtransmission is not included.

Meanwhile, when control information is transmitted in a PUSCH, channelcoding is independently performed on a CQI/PMI, an RI, and ACK/NACK,that is, the control information, at steps S126, S127, and S128. Thepieces of control information have different coding rates becausedifferent coded symbols are allocated for the transmission of thecontrol information.

In Time Division Duplex (TDD), ACK/NACK feedback mode supports two typesof ACK/NACK bundling mode and ACK/NACK multiplexing mode by theconfiguration of a higher layer. For ACK/NACK bundling, ACK/NACKinformation bits include 1 bit or 2 bits. For ACK/NACK multiplexing,ACK/NACK information bits include 1 bit to 4 bits.

After the concatenation between the CBs at step S124, the multiplexingof the coded bits f₀, f₁, f₂, f₃, . . . , f_(G-1) of the UL-SCH data andthe coded bits q₀, q₁, q₂, q₃, . . . , q_(N) _(L) _(·Q) _(CQt) ₋₁ of theCQI/PMI are performed at step S125. The results of the multiplexing ofthe UL-SCH data and the CQI/PMI are g₀, g₁, g₂, g₃, . . . , q_(II′-1).In this case, g_(i)(i=0, . . . , H′−1) is indicative of a column vectorhaving a length (Q_(m)·N_(L)). H=(G+N_(L)·Q_(CQI)) andH′=H/(N_(L)·Q_(m)). N_(L) is the number of layers to which an UL-SCHtransport block has been mapped. H is a total number of coded bitsallocated to the N_(L) transmission layers to which the transport blockhas been mapped for the UL-SCH data and CQI/PMI information.

Next, the multiplexed data and CQI/PMI and the separately channel-codedRI and ACK/NACK are subjected to channel interleaving, therebygenerating an output signal at step S129.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 13 shows the configuration of a known MIMO communication system.

Referring to FIG. 13, if the number of transmission (Tx) antennas isincreased to N_(T) and the number of reception (Rx) antennas isincreased to N_(R) at the same time, a theoretical channel transmissioncapacity is increased in proportion to the number of antennas, unlike inthe case where a plurality of antennas is used only in a transmitter ora receiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_(i) by a maximum transfer rate R_(o) if one antenna isused.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (NT×NR) of the number of transmissionantennas (NT) and the number of reception antennas (NR).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 13, it is assumed that N_(T) transmissionantennas and N_(R) reception antennas are present.

First, a transmission signal is described below. If the N_(T)transmission antennas are present as described above, a maximum numberof pieces of information which can be transmitted are N_(T), which maybe represented using the following vector.S=[S₁,S₂, . . . ,S_(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s₁, s₂, s_(NT). In this case, if pieces oftransmission power are P₁, P₂, . . . , P_(NT), transmission informationhaving controlled transmission power may be represented using thefollowing vector.ŝ=[ŝ₁,ŝ₂, . . . . ŝ_(N) _(T) ]^(T)=[P₁s₁,P₂s₂, . . . ,P_(N) _(T) s_(N)_(T) ]^(T)  [Equation 3]

Furthermore, ŝ may be represented as follows using the diagonal matrix Pof transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Meanwhile, the information vector ŝ having controlled transmission poweris multiplied by a weight matrix W, thus forming N_(T) transmissionsignals x₁, x₂, . . . , x_(NT) that are actually transmitted. In thiscase, the weight matrix functions to properly distribute thetransmission information to antennas according to a transport channelcondition. The following may be represented using the transmissionsignals x₁, x₂, . . . , x_(NT).

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

In this case, w_(ij) denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_(R) reception antennas are present, the reception signals y₁, y₂, .. . , y_(NR) of the respective antennas are represented as follows usinga vector y.y=[y₁,y₁, . . . ,y_(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_(ij). In this case, it is to be noted that in order of the index ofh_(ij), the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 14 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 14, a channel from a total of N_(T) transmissionantennas to a reception antenna i may be represented as follows.h_(i) ^(T)=[h_(i1),h_(i2), . . . ,h_(iN) _(T) ]  [Equation 7]

Furthermore, if all channels from the N_(T) transmission antenna toN_(R) reception antennas are represented through a matrix expression,such as Equation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n₁, n₂, . . . , n_(NR) added to the N_(R) receptionantennas, respectively, are represented using a vector as follows.n=[n₁,n₂, . . . ,n_(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_(R), and the number of columns becomes equal to the number oftransmission antennas N_(T). That is, the channel matrix H becomes anN_(R)×N_(T) matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission when signal is transmitted through a channel and amethod of transmitting signal known to both the transmission side andthe reception side is mostly used. The aforementioned signal is called apilot signal or Reference Signal (RS).

When data is transmitted/received using a multi-input/output antenna, achannel state between a transmission antenna and a reception antennaneeds to be detected in order to accurately receive a signal.Accordingly, each transmission antenna needs to have an individualreference signal.

A downlink reference signal includes a Common Reference Signal (CRS)shared by all UEs within one cell and a Dedicated Reference Signal (DRS)for specific UE. Information for demodulation and channel measurementmay be provided using such reference signals.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds indicators related to channel quality, such as a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI) and/or a RankIndicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of Channel State Information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. UE may receive information about whether a DRSis present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 15 illustrates a reference signal pattern mapped to a downlinkresource block pair in a wireless communication system to which anembodiment of the present invention may be applied.

Referring to FIG. 15, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped unit, may be represented in the formof one subframe in a time domain X 12 subcarriers in a frequency domain.That is, in a time axis (i.e., x axis), one resource block pair has alength of 14 OFDM symbols in the case of a normal Cyclic Prefix (CP)(FIG. 15a ) and has a length of 12 OFDM symbols in the case of anextended CP (FIG. 15b ). In the resource block lattice, ResourceElements (REs) indicated by “0”, “1”, “2”, and “3” mean the positions ofthe CRSs of antenna port indices “0”, “1”, “2”, and “3”, and REsindicated by “D” denotes the position of a DRS.

A CRS is described in detail below. The CRS is used to estimate thechannel of a physical antenna and is a reference signal which may bereceived by all UEs located in a cell in common The CRS is distributedto the entire frequency bandwidth. Furthermore, the CRS may be used forChannel Quality Information (CQI) and data demodulation.

The CRS is defined in various formats depending on an antenna array onthe transmission side (i.e., an eNB). In a 3GPP LTE system (e.g.,release-8), various antenna arrays are supported, and the transmissionside of a downlink signal has three types of antenna arrays, such as 3single transmission antennas, 2 transmission antennas, and 4transmission antennas. If an eNB uses a single transmission antenna,reference signals for a single antenna port are arrayed. If an eNB uses2 transmission antennas, reference signals for 2 transmission antennaports are arrayed using a Time Division Multiplexing

(TDM) method and/or a Frequency Division Multiplexing (FDM) method. Thatis, different time resources and/or different frequency resources areallocated so that reference signals for 2 antenna ports aredistinguished from each other.

Furthermore, if an eNB uses 4 transmission antennas, reference signalsfor 4 transmission antenna ports are arrayed using the TDM and/or FDMmethods. Channel information measured by the reception side (i.e., UE)of a downlink signal may be used to demodulate data transmitted using atransmission method, such as single transmission antenna transmission,transmission diversity, closed-loop spatial multiplexing, open-loopspatial multiplexing, or an multi-User-multi-input/output (MIMO)antennas.

If a multi-input/output antenna is supported, when a reference signal istransmitted by a specific antenna port, the reference signal istransmitted in the positions of resource elements specified depending onthe pattern of the reference signal and is not transmitted in thepositions of resource elements specified for other antenna ports. Thatis, reference signals between different antennas do not overlap.

A rule for mapping a CRS to a resource block is defined as follows.

$\begin{matrix}{{k = {{6m} + {( {v + v_{shift}} ){mod}\; 6}}}{l = \{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \{ {0,1} \}} \\1 & {{{if}\mspace{14mu} p} \in \{ {2,3} \}}\end{matrix}m} = 0},1,\ldots\mspace{11mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3( {n_{s}\mspace{14mu}{mod}\mspace{11mu} 2} )} & {{{{if}\mspace{14mu} p} = 2}\mspace{14mu}} \\{3 + {3( {n_{s}\mspace{14mu}{mod}\mspace{11mu} 2} )}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\;{mod}\; 6}} }}} }} & \lbrack {{Equation}\mspace{14mu} 12} \rbrack\end{matrix}$

In Equation 12, k and 1 denote a subcarrier index and a symbol index,respectively, and p denotes an antenna port. N_(symb) ^(DL) denotes thenumber of OFDM symbols in one downlink slot, and N_(RB) ^(DL) denotesthe number of radio resources allocated to downlink. n_(s) denotes aslot index, and N_(ID) ^(cell) denotes a cell ID. mod denotes modulooperation. The position of a reference signal is different depending ona value v_(shift) in a frequency domain. Since the value v_(shift)depends on a cell ID, the position of a reference signal has variousfrequency shift values depending on a cell.

More specifically, in order to improve channel estimation performancethrough a CRS, the position of a CRS may be shifted in a frequencydomain. For example, if reference signals are placed at an interval of 3subcarriers, reference signals in one cell are allocated to a 3k-thsubcarrier, and reference signals in the other cell are allocated to a(3k+1)-th subcarrier. From the point of view of a single antenna port,reference signals are arrayed at an interval of 6 resource elements in afrequency domain. Reference signals are spaced apart from referencesignals allocated in other antenna ports at an interval of 3 resourceelements.

In a time domain, reference signals are started from the symbol index 0of each slot and are arrayed at a constant interval. A time interval isdifferent defined depending on the length of a cyclic prefix. In thecase of a normal cyclic prefix, reference signals are placed in thesymbol indices 0 and 4 of a slot. In the case of an extended cyclicprefix, reference signals are placed in the symbol indices 0 and 3 of aslot. A reference signal for an antenna port that belongs to 2 antennaports and that has a maximum value is defined within one OFDM symbol.Accordingly, in the case of 4 transmission antenna transmission,reference signals for RS antenna ports 0 and 1 are placed in the symbolindices 0 and 4 of a slot (i.e., symbol indices 0 and 3 in the case ofan extended cyclic prefix), and reference signals for antenna ports 2and 3 are placed in the symbol index 1 of the slot. The positions ofreference signals for antenna ports 2 and 3 in a frequency domain arechanged in a second slot.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input/output antenna transmission, precoding weight usedfor specific UE is combined with a transport channel transmitted by eachtransmission antenna when the UE receives a reference signal and is usedto estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., release-8) supports a maximum of 4 transmissionantennas and uses a DRS for rank 1 beamforming The DRS for rank 1beamforming also indicates a reference signal for an antenna port index5.

A rule on which a DRS is mapped to a resource block is defined asfollows. Equation 13 illustrates a normal cyclic prefix, and Equation 14illustrates an extended cyclic prefix.

$\begin{matrix}{{k = {{( k^{\prime} ){mod}\mspace{11mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \{ {2,3} \}} \\{{4m^{\prime}} + {( {2 + v_{shift}} ){mod}\; 4}} & {{{if}\mspace{14mu} l} \in \{ {5,6} \}}\end{matrix}l} = \{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}{0\text{,}1} & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 0} \\{2\text{,}3} & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{11mu},{{{3N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 13} \rbrack \\{{k = {{( k^{\prime} ){mod}\mspace{11mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {( {2 + v_{shift}} ){mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \{ {{\begin{matrix}4 & {l^{\prime} \in \{ {0,2} \}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 0} \\{1\text{,}2} & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{11mu},{{{4N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 14} \rbrack\end{matrix}$

In Equations 12 to 14, k and p denote a subcarrier index and an antennaport, respectively. N_(RB) ^(DL), n_(s), and N_(ID) ^(cell) denote thenumber of RBs allocated to downlink, the number of slot indices, and thenumber of cell IDs. The position of an RS is different depending on thevalue v^(shift) from the point of view of a frequency domain.

In Equations 13 and 14, k and l denote a subcarrier index and a symbolindex, respectively, and p denotes an antenna port. N_(sc) ^(RB) denotesthe size of an RB in a frequency domain and is represented as the numberof subcarriers. n_(PRB) denotes the number of physical RBs. N_(RB)^(PDSCH) denotes the frequency bandwidth of an RB for PDSCHtransmission. n_(s) denotes the index of a slot, and N_(ID) ^(cell)denotes the ID of a cell. mod denotes modulo operation. The position ofa reference signal is different depending on the value v_(shift) in afrequency domain. Since the value v_(shift) depends on the ID of a cell,the position of a reference signal has various frequency shift valuesdepending on a cell.

Sounding Reference Signal (SRS)

An SRS is mostly used in the measurement of channel quality in order toperform uplink frequency-selective scheduling and is not related to thetransmission of uplink data and/or control information, but the presentinvention is not limited thereto. The SRS may be used for various otherpurposes for improving power control or various startup functions of UEswhich have not been recently scheduled. The startup functions mayinclude an initial Modulation and Coding Scheme (MCS), initial powercontrol for data transmission, a timing advance, and frequencysemi-selective scheduling, for example. In this case, the frequencysemi-selective scheduling means selectively allocating a frequencyresource to the first slot of a subframe and pseudo-randomly hopping toanother frequency in the second slot of the subframe and allocatingfrequency resources.

Furthermore, the SRS may be used to measure downlink channel quality,assuming that a radio channel is reciprocal between uplink and downlink.Such an assumption is particularly valid when the same frequencyspectrum is shared between uplink and downlink and in Time DivisionDuplex (TDD) systems separated in a time domain.

The subframes of an SRS transmitted by UE within a cell may berepresented by a cell-specific broadcasting signal. A 4-bitcell-specific parameter “srsSubframeConfiguration” indicates 15available subframe arrays in which an SRS may be transmitted thoughrespective radio frames. In accordance with such arrays, the flexibilityof control of SRS overhead can be provided according to a deploymentscenario.

A sixteenth array completely turns off the switch of an SRS within acell, which is mostly suitable for a serving cell which provides serviceto high-speed UEs.

FIG. 16 illustrates an uplink subframe including the symbols of aSounding Reference Signal (SRS) in a wireless communication system towhich an embodiment of the present invention may be applied.

Referring to FIG. 16, an SRS is always transmitted through the lastSC-FDMA symbol in an arrayed subframe. Accordingly, an SRS and DMRS areplaced in different SC-FDMA symbols. The transmission of PUSCH data isnot permitted in a specific SC-FDMA symbol for SRS transmission. As aresult, if sounding overhead is the highest, that is, although an SRSsymbol is included in all subframes, sounding overhead does not exceedabout 7%.

Each SRS symbol is generated based on a base sequence (i.e., a randomsequence or a sequence set based on Zadoff-Ch (ZC)) regarding a giventime unit and frequency bandwidth. All UEs within the same cell use thesame base sequence. In this case, the transmissions of SRSs from aplurality of UEs within the same cell in the same frequency bandwidthand the same time are orthogonal to each other by different cyclicshifts of a base sequence and are distinguished from each other.

SRS sequences from different cells may be distinguished from each otherbecause different base sequences are allocated to respective cells, butorthogonality between the different base sequences is not guaranteed.

Coordinated Multi-Point (CoMP) Transmission and Reception

In line with the demand of LTE-advanced, there has been proposed CoMPtransmission in order to improve system performance CoMP is also calledco-MIMO, collaborative MIMO, or network MIMO. CoMP is expected toimprove performance of UE located in a cell edge and to improve theaverage throughput of a cell (or sector).

In general, inter-cell interference deteriorates performance of UElocated in a cell edge and the average cell (or sector) efficiency in amulti-cell environment in which a frequency reuse factor is 1. In orderto reduce inter-cell interference, a simple passive method, such asFractional Frequency Reuse (FFR), has been applied to an LTE system sothat UE placed in a cell edge in an interference-limited environment hasproper performance efficiency. However, instead of reducing the use offrequency resources per cell, a method of reusing inter-cellinterference as a signal required to be received by UE or reducinginter-cell interference is more advantageous. In order to achieve theabove object, a CoMP transmission method may be used.

A CoMP method applicable to downlink may be divided into a JointProcessing (JP) method and a Coordinated Scheduling/Beamforming (CS/CB)method.

In the JP method, data may be used in each point (ie, eNB) of a CoMPunit. The CoMP unit means a set of eNBs used in the CoMP method. The JPmethod may be subdivided into a joint transmission method and a dynamiccell selection method.

The joint transmission method is a method of transmitting, by aplurality of points, that is, some or all of the points of a CoMP unit,signals through a PDSCH at the same time. That is, data transmitted toone UE is transmitted from a plurality of transmission points at thesame time. The quality of a signal transmitted to UE can be improvedcoherently or non-coherently and interference between the UE and anotherUE can be actively removed through such a joint transmission method.

The dynamic cell selection method is a method of sending a signal by onepoint of a CoMP unit through a PDSCH. That is, data transmitted to oneUE on a specific time is transmitted from one point, but is nottransmitted from another point within the CoMP unit to the UE. A pointat which data is transmitted to UE may be dynamically selected.

In accordance with the CS/CB method, a CoMP unit performs beamforming incooperation in order to send data to one UE. That is, data istransmitted to UE in a serving cell only, but userscheduling/beamforming may be determined through cooperation between aplurality of cells within a CoMP unit.

In some embodiments, CoMP reception means the reception of a signaltransmitted by cooperation between a plurality of points that aregeographically separated. A CoMP method which may be applied to uplinkmay be divided into a Joint Reception (JR) method and a CoordinatedScheduling/Beamforming (CS/CB) method.

The JR method is a method of receiving, by a plurality of points, thatis, some or all of the points of a CoMP unit, a signal transmittedthrough a PDSCH. In the CS/CB method, a signal transmitted through aPDSCH is received only at one point, but user scheduling/beamforming maybe determined through cooperation between a plurality of cells within aCoMP unit.

Relay Node (RN)

In a relay node, data transmitted/received between an eNB and UE istransferred through two different links (i.e., a backhaul link and anaccess link) An eNB may include a donor cell. A relay node is wirelesslyconnected to a radio access network through a donor cell.

In relation to the use of the bandwidth (or spectrum) of a relay node, acase where a backhaul link operates in the same frequency bandwidth asthat of an access link is called an “in-band”, and a case where abackhaul link and an access link operate in different frequencybandwidths is called an “out-band.” In both the in-band and theout-band, UE (hereinafter called “legacy UE”) operating in accordancewith an existing LTE system (e.g., release-8) needs to be able to accessa donor cell.

A relay node may be divided into a transparent relay node and anon-transparent relay node depending on whether UE recognizes a relaynode. The term “transparent” means whether UE communicates with anetwork through a relay node is not recognized. The term“non-transparent” means whether UE communicates with a network through arelay node is recognized.

In relation to control of a relay node, a relay node may be divided intoa relay node formed as part of a donor cell and a relay nodeautonomously controlling a cell.

A relay node formed as part of a donor cell may have a relay nodeidentity (relay ID), but does not have its own cell identity.

If at least part of Radio Resource Management (RRM) is controlled by aneNB belonging to a donor cell, it is called a relay node formed as partof a donor cell although the remaining parts of the RRM are placed inthe relay node. Such a relay node may support legacy UE. For example,various types of smart repeaters, decode-and-forward relays, and secondlayer (L2) relay nodes and a Type-2 relay node correspond to such arelay node.

In the case of a relay node autonomously controlling a cell, the relaynode controls one or a plurality of cells, and a unique physical layercell identity is provided to each of the cells controlled by the relaynode. Furthermore, the cells controlled by the relay node may use thesame RRM mechanism. From a viewpoint of UE, there is no differencebetween access to a cell controlled by a relay node and access to a cellcontrolled by a common eNB. A cell controlled by such a relay node cansupport legacy UE. For example, a self-backhauling relay node, a thirdlayer (L3) relay node, a Type-1 relay node, and a Type-la relay nodecorrespond to such a relay node.

The Type-1 relay node is an in-band relay node and controls a pluralityof cells, and each of the plurality of cells is seen by UE as a separatecell different from a donor cell. Furthermore, the plurality of cellshas different physical cell IDs (this is defined in LTE release-8), andthe relay node may send its own synchronization channel and referencesignal. In the case of one cell operation, UE directly may receivescheduling information and HARQ feedback from a relay node and send itsown control channels (e.g., a Scheduling Request (SR), a CQI, andACK/NACK) to the relay node. Furthermore, the Type-1 relay node is seenby legacy UE (i.e., UE operating in accordance with an LTE release-8system) as a legacy eNB (i.e., an eNB operating in accordance with anLTE release-8 system). That is, the Type-1 relay node has backwardcompatibility. Meanwhile, the Type-1 relay node is seen by UEs operatingin accordance with an LTE-A system as an eNB different from a legacyeNB, thereby being capable of providing improved performance.

The Type-1a relay node has the same characteristics as the Type-1 relaynode except that it operates in an out-band. The operation of theType-1a relay node may be configured so that an influence on a firstlayer (L1) operation is minimized

The Type-2 relay node is an in-band relay node, and it does not have aseparate physical cell ID and thus does not form a new cell. The Type-2relay node is transparent to legacy UE, and the legacy UE does notrecognize the presence of the Type-2 relay node. The Type-2 relay nodemay send a PDSCH, but does not send at least CRS and PDCCH.

In order to prevent a relay node from operating in in-band, someresources in a time-frequency domain may need to be reserved for abackhaul link and may be configured so that they are not used for anaccess link This is called resource partitioning.

A known principle in resource partitioning in a relay node may bedescribed as follows. Backhaul downlink and access downlink may bemultiplexed according to a Time Division Multiplexing (TDM) method onone carrier frequency (i.e., only one of a backhaul downlink and anaccess downlink in a specific time is activated). Likewise, backhauluplink and access uplink may be multiplexed according to a TDM method onone carrier frequency (i.e., only one of a backhaul uplink and an accessuplink in a specific time is activated).

In backhaul link multiplexing in FDD, backhaul downlink transmission maybe performed in a downlink frequency bandwidth, and the transmission ofa backhaul uplink may be performed in an uplink frequency bandwidth. Inbackhaul link multiplexing in TDD, backhaul downlink transmission may beperformed in a downlink subframe of an eNB and a relay node, and thetransmission of a backhaul uplink may be performed in an uplink subframeof an eNB and a relay node.

In the case of an in-band relay node, for example, when the reception ofa backhaul downlink from an eNB and the transmission of an accessdownlink to UE are performed in the same frequency bandwidth at the sametime, signal interference may be generated in the reception end of arelay node due to a signal transmitted by the transmission end of therelay node. That is, signal interference or RF jamming may be generatedin the RF front end of the relay node. Likewise, when the transmissionof a backhaul uplink to an eNB and the reception of an access uplinkfrom UE are performed in the same frequency bandwidth at the same time,signal interference may be generated.

Accordingly, in order for a relay node to send/receive signals in thesame frequency bandwidth at the same time, a sufficient separation needsto be provided between a reception signal and a transmission signal(e.g., that the reception signal and the transmission signal need to besufficiently separated geographically, such as that a transmissionantenna and a reception antenna are installed on the ground and in thegrave, respectively).

One method for solving such signal interference is to allow a relay nodeto operate in such a way as not to send a signal to UE while receiving asignal from a donor cell. That is, a gap is generated in transmissionfrom the relay node to the UE, and the UE (including legacy UE) isconfigured to not expect any transmission from the relay node during thegap. Such a gap may be configured by configuring a Multicast BroadcastSingle Frequency Network (MBSFN) subframe. FIG. 17 illustrates thesegmentation of a relay node resource in a wireless communication systemto which an embodiment of the present invention may be applied.

In FIG. 17, a first subframe is a common subframe, and a downlink (i.e.,access downlink) control signal and data are transmitted from a relaynode to UE in the first subframe. In contrast, a second subframe is anMBSFN subframe, and a control signal is transmitted from the relay nodeto the UE in the control region of the downlink subframe, but notransmission is performed from the relay node to the UE in the remainingregion of the downlink subframe. In this case, since legacy UE expectsthe transmission of a PDCCH in all downlink subframes (i.e., a relaynode needs to provide support so that legacy UEs within the region ofthe relay node perform measurement functions by receiving a PDCCH everysubframe), the PDCCH needs to be transmitted in all downlink subframesfor the correct operation of the legacy UE. Accordingly, the relay nodedoes not perform backhaul downlink reception, but needs to performaccess downlink transmission in the first N (N=1, 2 or 3) OFDM symbolperiod of a subframe (i.e., the second subframe) on the subframeconfigured for downlink (i.e., backhaul downlink) transmission from aneNB to the relay node. For this, the relay node may provide backwardcompatibility to serving legacy UE because a PDCCH is transmitted fromthe relay node to the UE in the control region of the second subframe.The relay node may receive transmission from the eNB while notransmission is performed from the relay node to the UE in the remainingregion of the second subframe. Accordingly, access downlink transmissionand backhaul downlink reception may not be performed at the same time inan in-band relay node through such a resource partitioning method.

The second subframe using an MBSFN subframe is described in detail. Thecontrol region of the second subframe may be said to be a relay nodenon-hearing period.

The relay node non-hearing interval means an interval in which a relaynode does not receive a backhaul downlink signal, but sends an accessdownlink signal. The interval may be configured to have a 1, 2 or 3 OFDMlength, such as that described above. A relay node performs accessdownlink transmission to UE in a relay node non-hearing interval, butmay perform backhaul downlink reception from an eNB in the remainingregion. In this case, time is taken for the relay node to switch fromtransmission mode to reception mode because the relay node is unable toperform transmission/reception in the same frequency bandwidth at thesame time. Accordingly, a Guard Time (GP) needs to be configured so thatthe relay node switches to transmission/reception mode in the first someinterval of a backhaul downlink reception region. Likewise, a guard timefor enabling the relay node to switch to reception/transmission mode maybe configured although the relay node operates in such a way as toreceive a backhaul downlink from the eNB and to send an access downlinkto the UE. The length of such a guard time may be set as a value in atime domain. For example, the length of the guard time may be set as a k(k≥1) time sample (Ts) value or may be set as one or more OFDM symbollength.

Alternatively, relay node backhaul downlink subframes may becontiguously configured, or the guard time of the last part of asubframe may not be defined or configured according to a specificsubframe timing alignment relationship. Such a guard time may be definedonly in a frequency domain configured for backhaul downlink subframetransmission in order to maintain backward compatibility (if a guardtime is configured in an access downlink interval, legacy UE cannot besupported). In a backhaul downlink reception interval other than theguard time, the relay node can receive a PDCCH and a PDSCH from the eNB.This may be represented by a relay-PDCCH (R-PDCCH) and a relay-PDSCH(R-PDSCH) in the meaning of a relay node-dedicated physical channel.

Channel State Information (CSI) Feedback

An MIMO method may be divided into an open-loop method and a closed-loopmethod. In the open-loop method, a transmission end performs MIMOtransmission without the feedback of CSI from an MIMO reception end. Inthe closed-loop MIMO method, a transmission end receives CSI fed back byan MIMO reception end and performs MIMO transmission. In the closed-loopMIMO method, in order to obtain the multiplexing gain of an MIMOtransmission antenna, each of a transmission end and a reception end mayperform beamforming based on CSI. A transmission end (e.g., an eNB) mayallocate an uplink control channel or an uplink shared channel to areception end (e.g., UE) so that a reception end (e.g., UE) is able tofeed CSI back.

The feedback CSI may include a Rank Indicator (RI), a Precoding MatrixIndex (PMI), and a Channel Quality Indicator (CQI).

The RI is information about a channel rank. The channel of a rank meansa maximum number of layers (or streams) in which different informationmay be transmitted through the same time-frequency resource. A rankvalue may be fed back in a longer cycle (i.e., less frequently) than aPMI and CQI because it is mostly determined by long term fading of achannel.

The PMI is information about a precoding matrix which is used intransmission from a transmission end and is a value into which thespatial characteristic of a channel is reflected. The term “precoding”means that a transmission layer is mapped to a transmission antenna, anda layer-antenna mapping relationship may be determined based on aprecoding matrix. The PMI corresponds to the PMI of an eNB, which ispreferred by UE based on a metric, such as a Signal-to-Interference plusNoise Ratio (SINR). In order to reduce feedback overhead of precodinginformation, a method of previously sharing, by a transmission end and areception end, a codebook including several precoding matrices andfeeding only an index indicative of a specific precoding matrix in thecorresponding codebook back may be used.

The CQI is information indicative of the intensity of channel or qualityof channel. The CQI may be represented as a predetermined MCScombination. That is, a CQI index that is fed back is indicative of acorresponding modulation scheme and coding rate. In general, the CQI isa value into which a reception SINR which may be obtained when an eNBconfigures a space channel using a PMI is reflected.

In a system (e.g., LTE-A system) supporting an extended antennaconfiguration, to obtain additional multi-user diversity using amulti-user-MIMO (MU-MIMO) method is taken into consideration. In theMU-MIMO method, an interference channel is present between UEsmultiplexed in an antenna region. Accordingly, it is necessary toprevent interference from occurring in another UE if an eNB performsdownlink transmission using CSI fed back by one UE of multiple users.Accordingly, in order for an MU-MIMO operation to be correctlyperformed, CSI having higher accuracy compared to a single user-MIMO(SU-MIMO) method needs to be fed back.

A new CSI feedback method using improved CSI including an existing RI,PMI, and CQI may be used so that more accurate CSI can be measured andreported as described above. For example, precoding information fed backby a reception end may be indicated by a combination of two PMIs. One(the first PMI) of the two PMIs has the attributes of a long term and/ora wideband and may be called W1. The other (the second PMI) of the twoPMIs has the attributes of a short term and/or a sub-band and may becalled W2. The final PMI may be determined by a combination (orfunction) of W1 and W2. For example, assuming that the final PMI is W,W=W1*W2 or W=W2*W1 may be defined.

In this case, the average characteristics of a channel in terms of thefrequency and/or time are reflected in W1. In other words, W1 may bedefined as CSI in which the characteristics of a long term channel interms of time are reflected, the characteristics of a wideband channelin terms of frequency are reflected, or the characteristics of a longterm channel in terms of time and a wideband channel in terms offrequency are incorporated. In order to simply represent suchcharacteristics of W1, W1 is called CSI of long term-wideband attributes(or a long term wideband PMI).

A channel characteristic that is instantaneous compared to W1 isreflected in W2. In other words, W2 may be defined as CSI in which thecharacteristics of a short term channel in terms of time are reflected,the characteristics of a sub-band channel in terms of frequency arereflected, or the characteristics of a short term channel in terms oftime and a sub-band channel in terms of frequency are reflected. Inorder to simply represent such characteristics of W2, W2 is called CSIof a short term-sub-band attributes (or a short term sub-band PMI).

In order for one final precoding matrix W to be determined based oninformation about 2 different attributes (e.g., W1 and W2) indicative ofa channel state, it is necessary to configure a separate codebookincluding precoding matrices indicative of channel information aboutattributes (i.e., a first codebook for W1 and a second codebook for W2).The form of a codebook configured as described above may be called ahierarchical codebook. Furthermore, to determine a codebook to befinally used using the hierarchical codebook may be called hierarchicalcodebook transformation.

If such a codebook is used, channel feedback of higher accuracy comparedto a case where a single codebook is used is made possible. Single cellMU-MIMO and/or multi-cell cooperation communication may be supportedusing channel feedback of higher accuracy as described above.

Enhanced PMI for MU-MIMO or CoMP

In a next-generation communication standard, such as LTE-A, there hasbeen proposed transmission schemes, such as MU-MIMO and CoMP, in orderto achieve a high transfer rate. In order to implement such improvedtransmission schemes, UE needs to feed more complicated and various CSIback to an eNB.

For example, in MU-MIMO, a CSI feedback method of uploading, by UE-A,the PMI (hereinafter called a “best companion PMI (BCPMI)”) of UE to bescheduled along with the UE-A, together with the desired PMI of theUE-A, when the UE-A selects a PMI is taken into consideration.

That is, when co-scheduled UE is used as a precoder in a precodingmatrix codebook, it calculates a BCPMI that provides less interferenceto UE-A and additionally feeds the calculated BCPMI back to an eNB.

The eNB schedules the UE-A and another UE which prefers BCPM (BestCompanion Precoding Matrix (BCPM) corresponding to a BCPMI) precodingusing the information.

A BCPMI feedback method is divided into explicit feedback and implicitfeedback depending on whether feedback payload is present or not.

First, there is an explicit feedback method having feedback payload.

In the explicit feedback method, UE-A determines a BCPMI within aprecoding matrix codebook and feeds the BCPMI back to an eNB through acontrol channel. In one method, UE-A may select an interference signalprecoding matrix that maximizes an estimated SINR within a codebook andfeed the interference signal precoding matrix back as a BCPMI value.

An advantage of the explicit feedback method is to select a BCPMI moreeffective in removing interference and to send the selected BCPMI. Thereason for this is that, assuming that each of all codewords within acodebook is one interference beam, UE determines a value most effectivein removing interference to be a BCPMI by performing comparison onmetrics, such as SINRs. A greater feedback payload size is requiredbecause candidate BCPMIs are increased as a codebook size is increased.

Second, there is an implicit feedback method not having feedbackpayload.

In the implicit feedback method, UE-A does not search a codebook for acodeword having the least interference and select the retrieved codebookas a BCPMI, but a corresponding BCPMI is statically determined once adesired PMI is determined In this case, a BCPMI may include vectorsorthogonal to the determined desired PMI.

The reason for this is that it is effective to reduce interference froman interference signal when desired PM is selected in directions otherthan the direction of a PM because the desired PM has been configured inthe direction in which the channel gain of a channel H can be maximizedin order to maximize a reception SINR. If the channel H is analyzed as aplurality of independent channels through Singular Value Decomposition(SVD), such a BCPMI decision method is further justified. A 4×4 channelH may be decomposed through SVD as in Equation 15 below.

$\begin{matrix}{H = {{ULV}^{H} = {{\begin{bmatrix}u_{1} & u_{2} & u_{3} & u_{4}\end{bmatrix}\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \lambda_{2} & 0 & 0 \\0 & 0 & \lambda_{3} & 0 \\0 & 0 & 0 & \lambda_{4}\end{bmatrix}}\begin{bmatrix}v_{1}^{H} \\v_{2}^{H} \\v_{3}^{H} \\v_{4}^{H}\end{bmatrix}}}} & \lbrack {{Equation}\mspace{14mu} 15} \rbrack\end{matrix}$

In Equation 15, U, V is a unitary matrix. u_(i), v_(i), and λ_(i) arethe 4×1 left singular vector, 4×1 right singular vector, and singularvalue of a channel H and are arranged in λ_(i)>λ_(i+1) in descendingorder. All channel gains which may be theoretically obtained if abeamforming matrix V is used in a transmission end and a beamformingmatrix U^(H) is used in a reception end can be obtained without a loss.

In the case of a rank 1, optimal performance may be obtained from thepoint of view of an SNR because a channel gain |λ₁|² is obtained when atransmission beamforming vector v₁ and a reception beamforming vector ulare used. For example, it is advantage for UE-A to select a PM mostsimilar to v₁ in the case of a rank 1. If a desired PM is ideallymatched up with v₁, an interference signal can be perfectly removedwithout a loss of a desired signal by setting a reception beam as u₁ andsetting the transmission beam of the interference signal in a directionorthogonal to the PM. If there is some difference between a desired PMand v₁ due to a quantization error, however, an interference signal maynot be perfectly removed without a loss of a desired signal because thetransmission beam of the interference signal set in the directionorthogonal to the PM is no longer the same as a beam orthogonal to v₁,but it may help control the interference signal if the quantizationerror is small.

As an example of implicit feedback, if an LTE codebook is used, a BCPMImay be statically determined to be a vector index orthogonal to a PMI.

In this case, it has been assumed that the number of transmissionantennas is 4 and UE which has fed the PMI back has a reception rank of1, and 3 vectors orthogonal to a desired PMI are represented as 3BCPMIs.

For example if a PMI is 3, a BCPMI is determined to be 0, 1, or 2. ThePMI and the BCPMI are indicative of the indices of a 4×1 vector codewordwithin a codebook. An eNB considers the BCPMI set (BCPMI=0, 1, 2) to bea valid precoding index for removing interference and uses some of orthe entire BCPMI set as the precoder of co-schedule UE.

An advantage of an implicit PMI is that there is no additional feedbackoverhead because a desired PMI and a BCPMI set are mapped in a 1:1 way.However, a BCPM dependent on desired PM may have an error in thedirection of an optimal interference removal beam due to thequantization error of the desired PM (i.e., a precoding matrixcorresponding to a PMI). If a quantization error is not present, all 3BCPMs represent interference beams (ideal interference beams) forperfectly removing interference. If a quantization error is present,however, there is a difference between the beam of each of the 3 BCPMsand an ideal interference beam.

Furthermore, a difference between the ideal interference beams of theBCPMs is the same in average, but may be different on a specific moment.For example, if a desired PMI=3, it may be effective to remove aninterference signal in order of BCPMIs 0, 1, and 2. In this case, thereis a possibility that an eNB unaware of a relative error between theBCPMIs 0, 1, and 2 may determine the BCPMI 2 having the greatest errorwith an ideal interference beam to be the beam of an interference signaland may perform communication in the state in which strong interferenceis present between co-scheduled UEs.

General (Device-to-Device) D2D Communication

In general, D2D communication is limitedly used as a term indicative ofcommunication between things or thing intelligence communication. In anembodiment of the present invention, however, D2D communication mayinclude all types of communication between a variety of types of deviceshaving a communication function, such as smart phones and personalcomputers, in addition to simple devices having a communicationfunction.

FIG. 18 is a diagram conceptually illustrating D2D communication in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 18a shows an existing communication method based on an eNB. UE1 maysend data to an eNB in uplink, and the eNB may send data to UE2 indownlink Such a communication method may be called an indirectcommunication method through an eNB. An Un link (i.e., a link betweeneNBs or a link between an eNB and a relay node, which may be called abackhaul link), that is, a link defined in an existing wirelesscommunication system, and/or an Uu link (i.e., a link between an eNB andUE or a link between a relay node and UE, which may be called an accesslink) may be related to the indirect communication method.

FIG. 18b shows a UE-to-UE communication method, that is, an example ofD2D communication. The exchange of data between UEs may be performedwithout the intervention of an eNB. Such a communication method may becalled a direct communication method between devices. The D2D directcommunication method has advantages of reduced latency and the use oflesser radio resources compared to the existing indirect communicationmethod through an eNB.

FIG. 19 shows an example of various scenarios of D2D communication towhich a method proposed in this specification may be applied.

A scenario for D2D communication may be basically divided into (1) anout-of-coverage network, (2) a partial-coverage network, and (3) anin-coverage network depending on where UE1 and UE2 are placed withincell coverage (i.e., in-coverage) and out of cell coverage (i.e.out-of-coverage).

The in-coverage network may be divided into an in-coverage-single-celland an in-coverage-multi-cell depending on the number of cellscorresponding to coverage of an eNB.

FIG. 19(a) shows an example of an out-of-coverage network scenario forD2D communication.

The out-of-coverage network scenario means that D2D communication isperformed between D2D UEs without control of an eNB.

From FIG. 19(a), it may be seen that only UE1 and UE2 are present andthe UE1 and the UE2 perform direct communication.

FIG. 19(b) shows an example of a partial-coverage network scenario forD2D communication.

The partial-coverage network scenario means that D2D communication isperformed between D2D UE placed within network coverage and D2D UEplaced out of the network coverage.

From FIG. 19(b), it may be seen that UE1 placed within network coverageand UE2 placed out of the network coverage perform communication.

FIG. 19(c) shows an example of an in-coverage-single-cell scenario, andFIG. 19(d) shows an example of an in-coverage-multi-cell scenario.

The in-coverage network scenario means that D2D UEs perform D2Dcommunication through control of an eNB within network coverage.

In FIG. 19(c), UE1 and UE2 are placed within the same network coverage(or cell) and perform D2D communication under the control of an eNB.

In FIG. 19(d), UE1 and UE2 are placed within network coverage, but areplaced within different network coverage. Furthermore, the UE1 and theUE2 perform D2D communication under the control of eNBs managing each ofnetwork coverage. D2D communication is described in more detail below.

D2D communication may be performed in the scenarios of FIG. 19, but maybe commonly performed within network coverage (in-coverage) and out ofnetwork coverage (out-of-coverage). A link used for D2D communication(i.e., direct communication between UEs) may be called a D2D link, adirectlink, or a sidelink, but is hereinafter generally called asidelink, for convenience of description.

Sidelink transmission may be performed in an uplink spectrum in the caseof FDD and may be performed in an uplink (or downlink) subframe in thecase of TDD. Time Division Multiplexing (TDM) may be used for themultiplexing of sidelink transmission and uplink transmission.

Sidelink transmission and uplink transmission are not occured at thesame time. Sidelink transmission is not occured in a sidelink subframewhich partially or generally overlaps an uplink subframe or UpPTS usedfor uplink transmission. Furthermore, the transmission and reception ofa sidelink are also not occured at the same time.

The structure of an uplink physical resource may be identically used asthe structure of a physical resource used for sidelink transmission.However, the last symbol of a sidelink subframe includes a guard periodand is not used for sidelink transmission.

A sidelink subframe may include an extended Cyclic Prefix (CP) or anormal CP.

D2D communication may be basically divided into discovery, directcommunication, and synchronization.

1) Discovery

D2D discovery may be applied within network coverage (including aninter-cell and an intra-cell). In inter-cell discovery, both synchronousand asynchronous cell deployments may be taken into consideration. D2Ddiscovery may be used for various commercial purposes, such asadvertising, issuing coupons, and finding friends, to UE within aproximity region.

If UE 1 has a role of sending a discovery message, the UE 1 sends adiscovery message, and UE 2 receives the discovery message. Thetransmission and reception roles of the UE 1 and the UE 2 may bechanged. Transmission from the UE 1 may be received by one or moreUE(s), such as the UE 2.

The discovery message may include a single MAC PDU. In this case, thesingle MAC PDU may include a UE ID and an application ID.

A physical sidelink discovery channel (PSDCH) may be defined as achannel for sending the discovery message. The structure of a PUSCH maybe reused as the structure of the PSDCH.

Two types Type 1 and Type 2 may be used as a resource allocation methodfor D2D discovery.

In the case of Type 1, an eNB may allocate a resource for sending adiscovery message in a non-UE-specific way.

To be specific, a radio resource pool comprising a plurality of subframesets and a plurality of resource block sets for transmitting andreceiving a discovery message within a specific period (in what follows,‘discovery period’) is allocated, and a discovery transmitting UEselects a specific resource within the radio resource pool in anarbitrary manner and transmits a discovery message.

The periodic discovery resource pool can be allocated for transmissionof a discovery signal in a semi-static manner. The configurationinformation of a discovery resource pool for discovery transmissionincludes a discovery period, a subframe set which can be used fortransmission of a discovery signal within the discovery period, andinformation about a resource block set. The configuration information ofthe discovery resource pool can be transmitted to the UE through upperlayer signaling. In the case of an in-coverage UE, the discoveryresource pool for discovery transmission is set up by an eNB and can beinformed to the UE through RRC signaling (for example, SystemInformation Block (SIB)).

The discovery resource pool allocated for discovery within one discoveryperiod can be multiplexed to a time-frequency resource block of the samesize through TDM and/or FDM scheme, where the time-frequency resourceblock of the same size can be called a ‘discovery resource’. A discoveryresource can be set as one subframe unit and include two PhysicalResource Blocks (PRBs) per slot in each subframe. One UE can use onediscovery resource for transmission of a discovery MAC PDU.

Also, a UE can transmit a discovery signal repeatedly within a discoveryperiod for transmission of one transport block. Transmission of a MACPDU by one UE can be repeated (for example, four times) contiguously ornon-contiguously within the discovery period (namely radio resourcepool). The transmission times of a discovery signal for one transmissionblock can be transmitted to the UE through upper layer signaling.

UE may randomly select a first discovery resource in a discoveryresource set which may be used for the repetitive transmission of an MACPDU and may determine the remaining discovery resources in relation tothe first discovery resource. For example, a specific pattern may bepreviously determined, and a next discovery resource may be determinedaccording to the predetermined specific pattern depending on theposition of a discovery resource first selected by UE. Alternatively, UEmay randomly select each discovery resource within a discovery resourceset which may be used for the repetitive transmission of an MAC PDU.

In the case of Type 2, a resource for discovery message transmission isallocated in a UE-specific way. Type 2 is subdivided into Type-2A andType-2B. Type-2A is a method of allocating, by an eNB, a resource at theinstance at which UE sends a discovery message within a discovery cycle,and Type-2B is a method of allocating resources semi-persistently.

In the case of Type-2B, RRC_CONNECTED UE requests an eNB to allocate aresource for the transmission of a D2D discovery message through RRCsignaling. Furthermore, the eNB may allocate the resource through RRCsignaling. When the UE transits to an RRC_IDLE state or when the eNBwithdraws resource allocation through RRC signaling, the UE releases themost recently allocated transmission resource. As described above, inthe case of Type-2B, a radio resource may be allocated through RRCsignaling, and the activation/deactivation of an allocated radioresource may be determined by a PDCCH.

A radio resource pool for receiving a discovery message may beconfigured by an eNB, and UE may be notified of the configured radioresource pool through RRC signaling (e.g., a System Information Block(SIB)).

Discovery message reception UE monitors both the aforementioneddiscovery resource pools of Type 1 and Type 2 in order to receive adiscovery message.

2) Direct Communication

The region to which D2D direct communication is applied includes anetwork coverage edge area (i.e., edge-of-coverage) in addition toinside and outside network coverage (i.e., in-coverage andout-of-coverage). D2D direct communication may be used for purposes,such as Public Safety (PS).

If UE 1 has a role of direct communication data transmission, the UE 1sends direct communication data, and UE 2 receives the directcommunication data. The transmission and reception roles of the UE 1 andthe UE 2 may be changed. The direct communication transmission from theUE 1 may be received by one or more UE(s), such as the UE 2.

D2D discovery and D2D communication may be independently defined withoutbeing associated with each other. That is, in groupcast and broadcastdirect communication, D2D discovery is not required. If D2D discoveryand D2D direct communication are independently defined as describedabove, UEs do not need to perceive adjacent UE. In other words, in thecase of groupcast and broadcast direct communication, all reception UEswithin a group are not required to be adjacent to each other.

A physical sidelink shared channel (PSSCH) may be defined as a channelfor sending D2D direct communication data. Furthermore, a physicalsidelink control channel (PSCCH) may be defined as a channel for sendingcontrol information (e.g., Scheduling Assignment (SA), a transmissionformat for direct communication data transmission, etc) for D2D directcommunication. The structure of a PUSCH may be reused as the structuresof the PSSCH and the PSCCH.

Two types of mode 1 and mode 2 may be used as a resource allocationmethod for D2D direct communication.

Mode 1 refers to a method of scheduling, by an eNB, data for D2D directcommunication by UE or a resource used for UE to send controlinformation. Mode 1 is applied to in-coverage.

An eNB configures a resource pool for D2D direct communication. In thiscase, the resource pool for D2D communication may be divided into acontrol information pool and a D2D data pool. When an eNB schedulescontrol information and a D2D data transmission resource within a poolconfigured for transmission D2D UE using a PDCCH or ePDCCH(enhancedPDCCH), the transmission D2D UE sends control information and D2D datausing the allocated resource.

Transmission UE requests a transmission resource from an eNB. The eNBschedules a resource for sending control information and D2D directcommunication data. That is, in the case of mode 1, the transmission UEneeds to be in the RRC_CONNECTED state in order to perform D2D directcommunication. The transmission UE sends a scheduling request to theeNB, and a Buffer Status Report (BSR) procedure is performed so that theeNB may determine the amount of resources requested by the transmissionUE. Reception UEs monitors a control information pool. When decodingcontrol information related to reception UE, the reception UE mayselectively decode D2D data transmission related to correspondingcontrol information. The reception UE may not decode a D2D data poolbased on a result of the decoding of the control information.

Mode 2 refers to a method of randomly selecting, by UE, a specificresource in a resource pool in order to send data or control informationfor D2D direct communication. Mode 2 is applied to out-of-coverageand/or edge-of-coverage.

In mode 2, a resource pool for sending control information and/or aresource pool for sending D2D direct communication data may bepre-configured or may be configured semi-statically. UE is supplied witha configured resource pool (time and frequency) and selects a resourcefor D2D communication transmission in the resource pool. That is, the UEmay select a resource for control information transmission in a controlinformation resource pool in order to send control information.Furthermore, the UE may select a resource in a data resource pool inorder to send D2D direct communication data.

In D2D broadcast communication, control information is transmitted bybroadcasting UE. Control information is explicitly and/or implicitlyindicative of the position of a resource for data reception in relationto a physical channel (i.e., a PSSCH) on which D2D direct communicationdata is carried.

3) Synchronization

A D2D Synchronization Signal/sequence (D2DSS) can be used by a UE toobtain time-frequency synchronization. In particular, since the eNB isunable to control a UE located beyond network coverage, a new signal andprocedure can be defined to establish synchronization among UEs. A D2Dsynchronization signal can be called a sidelink synchronization signal.

A UE transmitting a D2D synchronization signal periodically can becalled a D2D synchronization source or a sidelink synchronizationsource. In case a D2D synchronization source is an eNB, the structure ofa D2D synchronization signal being transmitted can be identical to thatof PSS/SSS. In case the D2D synchronization source is not an eNB (forexample, a UE or GNSS (Global Navigation Satellite System)), thestructure of a D2D synchronization signal being transmitted can be newlydefined. The D2D synchronization signal is transmitted periodically witha period not shorter than 40 ms. Each UE can have a physical-layer D2Dsynchronization identity. The physical-layer D2D synchronizationidentifier may be called a physical-layer sidelink synchronizationidentity or simply a D2D synchronization identifier.

The D2D synchronization signal includes a D2D primary synchronizationsignal/sequence and a D2D secondary synchronization signal/sequence.These signals can be called a primary sidelink synchronization signaland a secondary sidelink synchronization signal, respectively.

Before transmitting a D2D synchronization signal, the UE may firstsearch for a D2D synchronization source. If a D2D synchronization sourceis found, the UE can obtain time-frequency synchronization through a D2Dsynchronization signal received from the D2D synchronization sourcefound. And the corresponding UE can transmit the D2D synchronizationsignal.

In D2D communication, direct communication between two devices isdescribed below as an example, for clarity, but the scope of the presentinvention is not limited thereto. The same principle described in anembodiment of the present invention may be applied to D2D communicationbetween a plurality of two or more devices.

Distributed Discovery Method

One of D2D discovery methods includes a method (hereinafter called“distributed discovery”) of performing, by all UEs, discovery in adistributed way. The method of performing distributed D2D discoverymeans a method of autonomously determining, by all UEs, discoveryresources and sending and receiving discovery messages unlike a methodof determining resource selection at one place (e.g., an eNB, UE, or aD2D scheduling device) as in a centralized method.

Hereinafter, a signal (or message) periodically transmitted by UEs forD2D discovery may be hereinafter called a discovery message, discoverysignal, or beacon. The signal is generally called a discovery message,for convenience of description.

In distributed discovery, a dedicated resource may be periodicallyallocated as a resource for allowing UE to send and receive a discoverymessage, separately from a cellular resource. This is described belowwith reference to FIG. 21.

FIG. 20 shows an example in which discovery resources have beenallocated according to an embodiment of the present invention.

Referring to FIG. 20, in the distributed discovery method, a discoverysubframe (i.e., a “discovery resource pool”) 2001 for discovery in allcellular uplink frequency-time resources is allocated fixedly (ordedicatedly), and the remaining region may consist of an existing LTEuplink Wide Area Network (WAN) subframe region 2003. The discoveryresource pool may include one or more subframes.

The discovery resource pool may be periodically allocated at a specifictime interval (i.e., “discovery cycle”). Furthermore, the discoveryresource pool may be repeatedly configured within one discovery cycle.

FIG. 20 shows an example in which a discovery resource pool is allocatedin a discovery cycle of 10 sec and 64 contiguous subframes are allocatedto each discovery resource pool, but a discovery cycle and the size oftime/frequency resources of a discovery resource pool are not limitedthereto.

UE autonomously selects a resource (i.e., “discovery resource”) forsending its discovery message in a dedicated allocated discovery pooland sends the discovery message through the selected resource. This isdescribed below with reference to FIG. 21.

FIG. 21 is a simplified diagram illustrating a discovery processaccording to an embodiment of the present invention.

Referring to FIGS. 20 and 21, a discovery method basically includes a3-step procedure, such as a resource sensing step S2101 for discoverymessage transmission, a resource selection step S2103 for discoverymessage transmission, and a discovery message transmission and receptionstep S2105.

First, in the resource sensing step S2101 for discovery messagetransmission, all UEs performing D2D discovery receive (i.e., sense) alldiscovery messages in a distributed way (i.e., autonomously) during 1cycle (period) of a D2D discovery resource (i.e., a discovery resourcepool). For example, assuming that an uplink bandwidth is 10 MHz in FIG.20, all UEs receive (i.e., sense) all discovery messages transmitted inN=44 RBs (6 RBs of a total of 50 RBs are used for PUCCH transmissionbecause the entire uplink bandwidth is 10 MHz) during K=64 msec (64subframes).

Furthermore, in the resource selection step S2103 for discovery messagetransmission, UE selects resources that belong to the sensed resourcesand that have a low energy level and randomly selects a discoveryresource within a specific range (e.g., within lower x % (x=a specificinteger, 5, 7, 10, . . . )) from the selected resources.

A discovery resource may include one or more resource blocks having thesame size and may be multiplexed within a discovery resource pool in aTDM and/or FDM way.

The reason why the UE selects the resources having a low energy level asthe discovery resources may be considered to mean that UEs do not usethe same D2D discovery resource a lot nearby in the case of resources ofa low energy level. That is, this disprove that the number of UEsperforming D2D discovery procedures that causes interference is not manynearly. Accordingly, if resources having a low energy level are selectedas described above, there is every probability that interference issmall when a discovery message is transmitted.

Furthermore, the reason why a resource having the lowest energy level isnot selected, but discovery resources are randomly selected within apredetermined range (i.e., within lower x %) is that there is apossibility that if a resource having the lowest energy level isselected, several UEs may select the same resource corresponding to thelowest energy level at the same time. That is, a lot of interference maybe caused because UEs select the same resource corresponding to thelowest energy level. Accordingly, a discovery resource may be randomlyselected within a predetermined range (i.e., configuring a candidatepool for selectable resources). In this case, for example, the range ofthe energy level may be variably configured depending on the design of aD2D system.

Furthermore, in the discovery message transmission and reception stepS2105, that is, the last step, the UE sends and receives discoverymessages based on the discovery resource after a discovery cycle (afterP=10 seconds in FIG. 20) and periodically sends and receives discoverymessages depending on a random resource hopping pattern in subsequentdiscovery cycles.

Such a D2D discovery procedure continues to be performed even in anRRC_IDLE state not having connection with an eNB as well as in anRRC_CONNECTED state in which the UE has connection with the eNB.

If such a discovery method is taken into consideration, all UEs sensesall resources (i.e., discovery resource pools) transmitted bysurrounding UEs and randomly selects discovery resources from all thesensed resources within a specific range (e.g., within lower x %).

The above method has a disadvantage in that all resources being used byall UEs in addition to surrounding UEs must be received for D2Ddiscovery regardless of the distance between the UEs. That is, each UEis unable to be aware that it has to send a discovery message to whichplace because all UEs randomly select discovery resource. Accordingly,all the UEs has to determine whether to detect discovery resources bymonitoring whether a signal is present in corresponding resources overthe entire bandwidth and during the entire given time or has to attemptto detect the discovery resources. Practically, it is important to checkthat surrounding UEs rather than UE placed at a remote place senddiscovery messages through which discovery resources in order to sendresources for D2D discovery, but the positions of UEs are unaware in aD2D discovery step. Furthermore, a method of exchanging pieces ofposition information about all UEs between the UEs using a specificresource periodically is inefficient.

That is, there is an inefficient problem if all UEs receive the entireD2D discovery resource pool and sense the entire discovery resource poolin a lump as in the aforementioned method.

Hereinafter, an embodiment of the present invention proposes a method ofdetermining a discovery resource using a Reference Signal (RS).

In 3GPP LTE/LTE-A systems, in order to manage signaling connectionbetween UE and a network, an EPS Connection Management (ECM)-CONNECTEDstate and an ECM-IDLE state are defined. The ECM-CONNECTED state and theECM-IDLE state may be applied to UE and an MME. ECM connection includesRRC connection established between UE and an eNB and S1 signalingconnection established between an eNB and an MME. An RRC state indicateswhether the RRC layer of UE and the RRC layer of an eNB have beenlogically connected. That is, if the RRC layer of UE is connected to theRRC layer of an eNB, the UE is in an RRC-CONNECTED state. If the RRClayer of the UE is not connected to the RRC layer of the eNB, the UE isin an RRC-IDLE state.

A network is able to know the presence of UE in the ECM-CONNECTED statein a cell unit and effectively controlling the UE. That is, when the UEis in the ECM-CONNECTED state, the mobility of the UE is managed by acommand from the network. In the ECM-CONNECTED state, the network isaware of a cell to which the UE belongs. Accordingly, the network maysend and/or receive data to the UE and/or from the UE, may controlmobility, such as the handover of the UE, and may perform cellmeasurement on surrounding cells.

In contrast, a network is unable to know the presence of UE in theECM-IDLE state and a Core Network (CN) manages the UE in a tracking areaunit, that is, an area unit greater than a cell. When the UE is in theECM-IDLE state, the UE performs discontinuous reception (DRX) configuredby an NAS using an ID uniquely allocated in the tracking area. That is,the UE may receive the broadcasting of system information and paginginformation by monitoring a paging signal in a specific pagingopportunity for each UE-specific paging DRX cycle. Furthermore, when theUE is in the ECM-IDLE state, a network does not have context informationabout the UE. Accordingly, the UE in the ECM-IDLE state may perform amobility-related procedure based on the UE, such as cell selection orcell reselection, without a need to receive a command from the network.In the ECM-IDLE state, if the position of the UE is different from aposition known to the network, the UE may notify the network of theposition of the UE through a Tracking Area Update (TAU) procedure.

As described above, the D2D discovery procedure needs to continue to beperformed even in the RRC_IDLE state in which UE does not haveconnection with an eNB as well as in the RRC_CONNECTED state in whichthe UE has connection with the eNB.

In 3GPP LTE/LTE-A systems, all UEs continue to receive a ReferenceSignal (RS) periodically broadcasted by an eNB within a cell in downlinkAfter being powered on, UE receives an RS regardless of theRRC_CONNECTED state or the RRC_IDLE state.

UE in the RRC_IDLE state continues to perform cell selection (or cellreselection) based on an RS as they move. If the UE moves out of aTracking Area (TA) including several cells, it performs a TA updateprocedure over a network. UE in the RRC_CONNECTED state performs ahandover procedure based on an RS when it moves between eNBs in thestate in which the UE has connection with an eNB. This is described indetail below with reference to FIG. 22.

FIG. 22 is a diagram illustrating UEs for receiving a reference signalaccording to an embodiment of the present invention.

Referring to FIG. 22, all UEs periodically receive an RS from an eNB andcalculate Reference Signal Received Power (RSRP) based on the receivedRS. If the UEs are placed at the center of the eNB and receive strong RSin the state in which they are close to the eNB, high reception powerappears. That is, RSRP is measured as being a high value.

If UE moves to the coverage edge area of the eNB and the distancebetween the eNB and the UE becomes distant, the intensity of the RSreceived by the UE through pathloss becomes weak. That is, RSRP ismeasured as being a low value. If the UE moves toward the edge of theeNB during such a process of continuing to receive the RS and measuredRSRP becomes lower than a predetermined reception threshold, the UEreceives the RSs of surrounding eNBs and performs cell reselection or ahandover procedure depending on its RRC state.

Such a TA update or handover procedure is performed separately from aD2D discovery process in which uplink is used, and it continues to beperformed as the UE moves through downlink

In the example of FIG. 22, it is assumed that reception power of RStransmitted from an eNB is 60 dbm at the center of a cell closest to theeNB and is −60 dbm near a cell edge farthest from the eNB. It is assumedthat in the case of UE 1, reception power of the RS is 30 dbm becausethe UE1 is placed close to the eNB, in the case of UE 2 and UE 4,reception power of the RS is 0 dbm because the UE2 and the UE4 areplaced in the middle of the eNB and the cell edge, and in the case of UE3, reception power of the RS is −30 dbm because the UE3 is placed nearthe cell edge.

If UEs have similar RSRP values as described above, this means that thepathloss of an RS may be present near the position where the UEs areplaced if the pathloss of the RS is taken into consideration. That is,there is a good possibility that the UEs may be concentrically presentaround an eNB or around UE which sends the RS. In other words, there isa high probability that UEs having similar RSRP may be adjacent to eachother in position.

D2D discovery may be performed mainly for surrounding UEs. Accordingly,if such RSRP information is used, UEs may perform D2D discovery mainlyfor surrounding UEs even without the exchange of position informationthrough the Global Positioning Systems (GPSs) of the UEs or the exchangeof position information between UEs for discovery.

Hereinafter, an embodiment of the present invention proposes a method ofdetermining, by UE, a specific resource area to be sensed within a D2Ddiscovery resource pool based on cell measurement results measured usinga received RS (e.g., a CRS or a CSI-RS) and selecting a discoveryresource in the specific resource area. In this case, the cellmeasurement results include measured results, such as Radio LinkMonitoring (RLM), Radio Resource Management (RRM) (e.g., RSRP, ReferenceSignal Received Quality (RSRQ), a Received Signal Strength Indicator(RSSI)), Channel State Information (CSI) (e.g., a CQI, a PMI, and anRI), and pathloss.

If a D2D discovery resource area is allocated based on signalinformation transmitted by a network using the method proposed by anembodiment of the present invention as described above, a sensingduration can be reduced and surrounding UEs can be discovered morerapidly and efficiently.

FIG. 23 is a diagram illustrating a method for sensing a D2D discoverymessage according to an embodiment of the present invention.

Referring to FIG. 23, UE receives discovery resource area configurationinformation from an eNB at step S2301.

In this case, the discovery resource area means a candidate region,which is sensed in order for the UE to select a discovery resource in adiscovery resource pool based on measured cell measurement informationand in which the UE selects the discovery resource. In other words, thediscovery resource pool means a resource area which is used by UEs,grouped based on cell measurement information, for a discovery procedureby group.

The discovery resource area may be determined to be divided (orsegmented) into a combination of one or more of a frequency domain, atime domain, and a partial region. For example, in the example of FIG.20, assuming that an uplink bandwidth is 10 MHz, a total of 44 RBs areused as a discovery resource pool, and a discovery resource area issegmented in a frequency domain, 4 discovery resource areas may beconfigured every 11 RBs in the frequency domain. Furthermore, in theexample of FIG. 20, assuming that 64 subframes are used as a discoveryresource pool and a discovery resource area is segmented in a timedomain, 4 discovery resource areas may be configured every 16 subframesin the time domain. A method for configuring a discovery resource areais described in more detail below.

Such a discovery resource area may be dynamically configured for eachdiscovery resource pool. Alternatively, the discovery resource area maybe semi-statically configured by one or more discovery cycles.

Furthermore, the discovery resource area may be configured in acell-specific way and applied to UEs belonging to a corresponding cellin common or may be configured to each UE in a UE-specific way.

Configuration information about a discovery resource area configured asdescribed above may be periodically broadcasted to UE as systeminformation, such as a System Information Block (SIB) or a MasterInformation Block (MIB). Furthermore, the configuration information maybe transmitted to the UE through RRC signaling or a physical layerchannel (e.g., a PDCCH or PDSCH).

Configuration information about a discovery resource area meansinformation indicative of the relationship (i.e., mapping information)between cell measurement information measured by UE and the discoveryresource area. Furthermore, the configuration information may berepresented in the form of an equation or rule for determining thediscovery resource area based on cell measurement information calculatedby the UE. For example, if the region of a resource is allocated basedon a specific RSRP value, information indicating that a discoveryresource area is used according to the range of RSRP based on an RBindex No. 22 in the case of RSRP 0 dbm may be transmitted to an eNB.

More specifically, the mapping relationship (or equation or rule)between a discovery resource area and a cell measurement value (or therange of a cell measurement value) corresponding to the discoveryresource area is described below. For example, it is assumed that anuplink frequency domain is 10 MHz, 44 RBs (e.g., an RB index No. 4 to anRB index No. 47) of a total of 50 RBs (e.g., an RB index No. 1 to an RBindex No. 50) are configured as a discovery resource pool in a frequencydomain, and a discovery resource area is sorted based on RSRP in thefrequency domain. In this case, mapping information (or an equation orrule indicative of such a relationship), indicating that the discoveryresource area is determined to be a group A (from the RB index No. 4 tothe RB index No. 18) if a measured value of RSRP corresponds to a range“a” (e.g., −60 dbm or more to less than −20 dbm), the discovery resourcearea is determined to be a group B (from the RB index No. 19 to the RBindex No. 32) if the measured value of RSRP corresponds to a range “b”(−20 dbm or more to less than 20 dbm), and the discovery resource areais determined to be a group C (from the RB index No. 33 to the RB indexNo. 47) if the measured value of RSRP corresponds to a range “c” (20 dbmor more to 60 dbm or less), may be transmitted to the UE.

In this case, a cell measurement value (or the range of a cellmeasurement value or threshold) may be represented as follows.

In the example of FIG. 22, it is assumed that an RSRP value has a rangefrom a maximum of 60 dbm to a minimum of −60 dbm and the range of RSRPis set as −60 dbm or more to less than −20 dbm, −20 dbm or more to lessthan 20 dbm, and 20 dbm or more to 60 dbm.

In this case, a value, that is, the reference point of each RSRP range,and a value for specifying a range of RSRP to which each reference pointbelongs may be used. For example, −40 dbm, 0 dbm, and 40 dbm may betransmitted to the UE as values, that is, the respective referencepoints of the RSRP ranges. 40 dbm (or 20 dbm (if higher and lower valuesare the same)) may be transmitted to the UE as a value for specifying arange of RSRP to which each reference point belongs.

Furthermore, the start value of the entire RSRP range and a value forindicating each RSRP range may be used. For example, −60 dbm may betransmitted to the UE as the start value of the entire RSRP range, and40 dbm may be transmitted to the UE as the value for indicating eachrange. In this case, the UE may recognize that the RSRP range is setevery 40 dbm starting from −60 dbm.

Furthermore, only the start value of each RSRP range may be used. Forexample, −60 dbm, −20 dbm, and 20 dbm may be transmitted to the UE asthe respective start values of the RSRP ranges. In this case, the UE mayrecognize that the RSRP ranges are set to −60 dbm or more to less than−20 dbm, −20 dbm or more to less than 20 dbm, and 20 dbm or more to 60dbm, respectively.

Furthermore, information for specifying the discovery resource area maybe represented as follows. It is assumed that an uplink frequency domainis 10 MHz, 44 RBs of a total of 50 RBs are configured as a discoveryresource pool in a frequency domain, and a discovery resource area isconfigured every 11 RBs in the frequency domain.

In this case, a resource index, that is, the reference point of eachdiscovery resource area, and information for specifying the range of adiscovery resource area to which each reference point belongs may beused. For example, the RB index No. 9, the RB index No. 20, the RB indexNo. 31, and the RB index No. 42 may be transmitted to the UE asrespective resource indices, that is, the reference points of discoveryresource areas. 11 RBs (or 5 RBs if higher and lower values are thesame) may be transmitted to the UE as the range of a discovery resourcearea to which each reference point belongs.

Furthermore, a resource index at which the entire discovery resourcearea is started and information for indicating the range of eachdiscovery resource area may be used. For example, the RB index No. 4 maybe transmitted to the UE as a resource index at which the entirediscovery resource area is started. 11 RBs may be transmitted to the UEas information for indicating the range of each discovery resource area.In this case, the UE may recognize that a discovery resource area hasbeen configured every 11 RBs starting from the RB index No. 4.

Furthermore, only a resource index at which each discovery resource areais started may be used. For example, the RB index No. 4, the RB indexNo. 15, the RB index No. 26, and the RB index No. 37 may be transmittedto the UE as resource indices at which respective discovery resourceareas are started. In this case, the UE may recognize that the discoveryresource areas are configured from the RB index No. 4 to the RB indexNo. 14, from the RB index No. 15 to the RB index No. 25, from the RBindex No. 26 to the RB index No. 36, and from the RB index No. 37 to theRB index No. 47, respectively.

At step S2303, the UE receives an RS periodically transmitted by the eNBand measures a cell based on the RS. Furthermore, the UE determines adiscovery resource area to which the UE belongs based on the calculatedcell measurement information and the discovery resource areaconfiguration information received at step S2301.

In this case, the UE may determine the discovery resource area to whichthe UE belongs based on a value measured using a signal (e.g., adiscovery message or a synchronization signal) transmitted by another UEother than the RS transmitted by the eNB and the discovery resource areaconfiguration information received at step S2301.

Furthermore, the UE may determine the discovery resource area by takinginto consideration both the value measured using a signal transmitted bythe eNB or another UE and a cell recognizer/identifier.

The UE senses a discovery resource within the determined discoveryresource area at step S2305. That is, the UE receives (i.e., senses) alldiscovery messages transmitted in the discovery resource area determinedat step S2303.

At step S2307, the UE selects a resource for discovery messagetransmission within the discovery resource area determined at stepS2303.

The UE searches the resources, sensed at step S2305, for resourceshaving a low energy level and randomly selects a discovery resourcewithin a specific range (e.g., low x % (x=a specific integer, 5, 7, 10,. . . )) in the retrieved resources.

Furthermore, the UE may receive a subframe configuration set, allocatedby the eNB, for sending a discovery message and select the discoveryresource randomly or based on a specific probability within theallocated subframe configuration set.

The UE transmits the discovery message in the selected discoveryresource at step S2309. Furthermore, in a subsequent discovery cycle,the UE periodically sends and receives a discovery message according toa random resource hopping pattern.

A method for configuring a discovery resource area is described indetail below with reference to drawings.

An embodiment in which UE configures a discovery resource area based onmeasured RSRP using a CRS transmitted by an eNB is mostly describedbelow, for convenience of description, but the present invention is notlimited thereto.

FIG. 24 shows an example in which discovery resource areas aredistinctly configured according to an embodiment of the presentinvention.

In FIG. 24, small squares indicate discovery resources now used by otherUEs, and different patterns of the squares indicate that the discoveryresources are used by different UEs.

In FIG. 24, it is assumed that a discovery resource pool 2401 isconfigured to include 44 RB pairs in a frequency domain and configuredto include 64 subframes in a time domain. Furthermore, it is assumedthat the discovery resource pool 2401 is divided into discovery resourceareas based on subbands in the frequency domain based on the RSRP valuesof RSs received by UEs. Furthermore, as in FIG. 22, it is assumed thatthree UEs are present and each discovery resource area is divided intothree frequency domains for each UE. Furthermore, as in FIG. 22, it isassumed that if the entire range of RSRP is −60 dbm to 60 dbm in acorresponding cell, RSRP ranges mapped to the respective discoveryresource area are −60 dbm˜−30 dbm, −30 dbm 18 30 dbm, and 30 dbm˜60 dbm.

Referring to FIG. 24, in the case of UE1, RSRP of the received RS mayhave a value of about 60 dbm because the UE1 is placed at the center ofan eNB. In this case, the UE1 may configure a resource area, mapped tothe RSRP range of 30 dbm˜60 dbm, as a sensing window (i.e., a discoveryresource area A) 2403. That is, UEs having the RSRP measurement value of30 dbm˜60 dbm are determined to be placed in the discovery resource areaA 2403 mapped to the RSRP measurement value of 30 dbm˜60 dbm.

Furthermore, in the case of UE2, RSRP of the received RS may have avalue of about 0 dbm because the UE2 is placed at a point furtherdistant from the center of the eNB. In this case, the UE2 may configurea resource area, mapped to the RSRP range of −30 dbm˜30 dbm, as adiscovery resource area B 2405. That is, UEs having the RSRP measurementvalue of −30 dbm˜30 dbm are determined to be placed in the discoveryresource area B 2405 mapped to the RSRP measurement value of −30 dbm˜30dbm.

Furthermore, in the case of UE3, RSRP of the received RS may have avalue of about −60 dbm because the UE3 is placed in the coverage edge ofthe eNB. In this case, the UE3 may configure a resource area, mapped tothe RSRP range of −60 dbm˜−30 dbm, as a discovery resource area C 2407.That is, UEs having the RSRP measurement value of −60 dbm˜−30 dbm aredetermined to be placed in the discovery resource area C 2407 mapped tothe RSRP measurement value of −60 dbm˜−30 dbm.

Furthermore, each UE senses a discovery message resource within theconfigured discovery resource area (or sensing window) range and selectsa discovery resource for sending its discovery message within thediscovery resource area (or sensing window) range.

In FIG. 24, the discovery resource areas have been illustrated as beingcontiguously configured in the frequency domain, but they may not becontiguously (e.g., a discontiguous RB group) configured in thefrequency domain.

Furthermore, in FIG. 24, the discovery resource areas have beenillustrated as not overlapping, but the present invention is not limitedthereto. Adjacent discovery resource areas may overlap.

In the method proposed with reference to FIG. 24, UEs have beenillustrated as being grouped based on RSRP. In some embodiments, UEs maybe grouped by taking into consideration a cell recognizer/identifier(e.g., a cell ID) along with RSRP with consideration taken of theoperation of UE for performing discovery (or direct communication) withanother cell. That is, UEs may be grouped by taking into considerationthat corresponding UE belongs to which cell along with RSRP measured bythe UE when the UE forms a group. Accordingly, in general, in the caseof UE placed at the center of a cell, grouping is performed by takinginto consideration a corresponding cell ID having strong RSRP. However,in the case of UE placed at the edge of the cell, grouping may beperformed by taking into consideration a neighbor cell ID along withRSRP of the UE.

More specifically, assuming that multiple cells have been synchronized,a cell ID may be used as the factor of a grouping rule function forresource selection. For example, discovery resource areas may beconfigured by forming groups in such a manner that a cell 1 isdetermined to be a group 1 if the cell 1 (in particular, in the case ofUE placed at the edge of a cell) has maximum RSRP and a cell 2 isdetermined to be a group 2 if the cell 2 has maximum RSRP.

Referring back to the example of FIG. 24, if RSRP of the RS of a cell towhich UE now belongs is a maximum, the discovery resource area A 2403and the discovery resource area B 2405 may be allocated. If RSRP of theRS of a neighbor cell is a maximum, the discovery resource area C 2407may be allocated. Furthermore, which one of the discovery resource areaA 2403 and the discovery resource area B 2405 will be determined may bedetermined based on the value of RSRP of the RS of a cell to which UEnow belongs.

In some embodiments, a UE grouping rule may be determined by performingcomparison on received RSRP thresholds instead of a cell ID. In otherwords, a case where RSRP is a predetermined threshold or more may bedefined to be included in a group Ai (i=1, 2, 3, . . . ) and a casewhere RSRP is less than the predetermined threshold may be defined to beincluded in a group Bi (i=1, 2, 3, . . . ) regardless of a cell ID (whenthe number of UE groups (i.e., discovery resource areas) is plural). Forexample, if the number of UE groups is 4, the number of groups used byUEs placed at the centers of respective cells may be defined to be 3 andthe number of groups used by UEs placed at the edges of the cells may bedefined to be 1 based on RSRP values, and discovery resource areas maybe selected.

In the example of FIG. 24, assuming that a predetermined threshold is−30 dbm, the discovery resource area A 2403 and the discovery resourcearea B 2405 may be allocated to UEs placed at the centers of cells.Furthermore, the discovery resource area C 2407 may be allocated to UEsplaced at the edge area of the cell.

Furthermore, if 5 UE groups are defined by taking into considerationdiscovery between multiple cells and UEs are included in the groups, 4of the 5 UE groups may include UEs slightly closer to cell centers, andthe remaining one UE group may include UEs placed cell edges and UEsplaced at the edge of a neighbor cell. That is, if discovery betweenmultiple cells is taken into consideration, a group to which UE at acell edge belongs may include UE (in particular, UE close in distance)placed at the cell edge of a neighbor cell (e.g., a cell selected basedon the intensity of a synchronization signal and/or the intensity ofRSRP) in addition to UE belonging to the same cell. That is, inter-celldiscovery is possible (on the assumption of synchronization betweencells) because UEs placed in the edge area of a neighbor cell havemutual proximity although they belong to different cells. Accordingly,UEs belonging to different cells may be defined as one group.Accordingly, a discovery message can be transmitted in the samediscovery resource area, and adjacent UE can be discovered by searchingfor a corresponding discovery resource area from the point of view ofreception.

In the example of FIG. 24, the discovery resource area A 2403 and thediscovery resource area B 2405 may be allocated to UEs placed in thecenters of cells. Furthermore, the discovery resource area C 2407 may beallocated to UE placed in a cell edge area and UE placed at the edgearea of a neighbor cell.

FIG. 25 shows an example in which discovery resource areas aredistinctly configured according to an embodiment of the presentinvention.

In FIG. 25, small squares indicate discovery resources now used by otherUEs, and different patterns of the squares indicate that the discoveryresources are used by different UEs.

In FIG. 25, it is assumed that a discovery resource pool 2501 isconfigured to include 44 RB pairs in a frequency domain and configuredto include 64 subframes in a time domain. Furthermore, it is assumedthat the discovery resource pool 2501 is divided into discovery resourceareas for each slot in the time domain based on the RSRP values of RSsreceived by UEs. Furthermore, as in FIG. 22, it is assumed that threeUEs are present and each discovery resource area is divided into threetime domains for each UE. Furthermore, as in FIG. 22, it is assumed thatif the entire range of RSRP is −60 dbm to 60 dbm in a correspondingcell, RSRP ranges mapped to the respective discovery resource area are−60 dbm˜−30 dbm, −30 dbm˜30 dbm, and 30 dbm˜60 dbm.

Referring to FIG. 25, in the case of UE1, RSRP of the received RS mayhave a value of about 60 dbm because the UE1 is placed at the center ofan eNB. In this case, the UE1 may configure a resource area (i.e., afirst slot interval), mapped to the RSRP range of 30 dbm˜60 dbm, as asensing window (i.e., a discovery resource area A) 2503. That is, UEshaving the RSRP measurement value of 30 dbm˜60 dbm are determined to beplaced in the discovery resource area A 2503 mapped to the RSRPmeasurement value of 30 dbm˜60 dbm.

Furthermore, in the case of UE2, RSRP of the received RS may have avalue of about 0 dbm because the UE2 is placed at a point furtherdistant from the center of the eNB. In this case, the UE2 may configureda resource area (i.e., a second slot interval), mapped to the RSRP rangeof −30 dbm˜30 dbm, as a discovery resource area B 2505. That is, UEshaving the RSRP measurement value of −30 dbm˜30 dbm are determined to beplaced in the discovery resource area B 2505 mapped to the RSRPmeasurement value of −30 dbm˜30 dbm.

Furthermore, in the case of UE3, RSRP of the received RS may have avalue of about −60 dbm because the UE3 is placed in the coverage edge ofthe eNB. In this case, the UE3 may configure a resource area (i.e., athird slot interval), mapped to the RSRP range of −60 dbm˜−30 dbm, as adiscovery resource area C 2507. That is, UEs having the RSRP measurementvalue of −60 dbm˜−30 dbm are determined to be placed in the discoveryresource area C 2507 mapped to the RSRP measurement value of −60 dbm˜−30dbm.

Furthermore, each UE senses a discovery message resource within theconfigured discovery resource area (or sensing window) range and selectsa discovery resource for sending its discovery message within thediscovery resource area (or sensing window) range.

In FIG. 25, the discovery resource areas have been illustrated as beingcontiguously configured in the time domain, but they may not becontiguously (e.g., a discontiguous RB group) configured in the timedomain.

Furthermore, in FIG. 25, the discovery resource areas have beenillustrated as not overlapping, but the present invention is not limitedthereto. Adjacent discovery resource areas may overlap.

In the method proposed with reference to FIG. 25, UEs have beenillustrated as being grouped based on RSRP. In some embodiments, UEs maybe grouped by taking into consideration a cell recognizer/identifier(e.g., a cell ID) along with RSRP with consideration taken of theoperation of UE for performing discovery (or direct communication) withanother cell. That is, UEs may be grouped by taking into considerationthat corresponding UE belongs to which cell along with RSRP measured bythe UE when the UE forms a group. Accordingly, in general, in the caseof UE placed at the center of a cell, grouping is performed by takinginto consideration a corresponding cell ID having strong RSRP. However,in the case of UE placed at the edge of the cell, grouping may beperformed by taking into consideration a neighbor cell ID along withRSRP of the UE.

More specifically, assuming that multiple cells have been synchronized,a cell ID may be used as the factor of a grouping rule function forresource selection. For example, discovery resource areas may beconfigured by forming groups in such a manner that a cell 1 isdetermined to be a group 1 if the cell 1 (in particular, in the case ofUE placed at the edge of a cell) has maximum RSRP and a cell 2 isdetermined to be a group 2 if the cell 2 has maximum RSRP.

Referring back to the example of FIG. 25, if RSRP of the RS of a cell towhich UE now belongs is a maximum, the discovery resource area A 2503and the discovery resource area B 2505 may be allocated. If RSRP of theRS of a neighbor cell is a maximum, the discovery resource area C 2507may be allocated. Furthermore, which one of the discovery resource areaA 2503 and the discovery resource area B 2505 will be determined may bedetermined based on the value of RSRP of the RS of a cell to which UEnow belongs.

In some embodiments, a UE grouping rule may be determined by performingcomparison on received RSRP thresholds instead of a cell ID. In otherwords, a case where RSRP is a predetermined threshold or more may bedefined to be included in a group Ai (i=1, 2, 3, . . . ) and a casewhere RSRP is less than the predetermined threshold may be defined to beincluded in a group Bi (i=1, 2, 3, . . . ) regardless of a cell ID (whenthe number of UE groups (i.e., discovery resource areas) is plural).

In the example of FIG. 25, assuming that a predetermined threshold is−30 dbm, the discovery resource area A 2503 and the discovery resourcearea B 2505 may be allocated to UEs placed at the centers of cells.Furthermore, the discovery resource area C 2507 may be allocated to UEsplaced at the edge area of the cell.

Furthermore, if 5 UE groups are defined by taking into considerationdiscovery between multiple cells and UEs are included in the groups, 4of the 5 UE groups may include UEs slightly closer to cell centers, andthe remaining one UE group may include UEs placed cell edges and UEsplaced at the edge of a neighbor cell. That is, if discovery betweenmultiple cells is taken into consideration, a group to which UE at acell edge belongs may include UE (in particular, UE close in distance)placed at the cell edge of a neighbor cell (e.g., a cell selected basedon the intensity of a synchronization signal and/or the intensity ofRSRP) in addition to UE belonging to the same cell. That is, inter-celldiscovery is possible (on the assumption of synchronization betweencells) because UEs placed in the edge area of a neighbor cell havemutual proximity although they belong to different cells. Accordingly,UEs belonging to different cells may be defined as one group.Accordingly, a discovery message can be transmitted in the samediscovery resource area, and adjacent UE can be discovered by searchingfor a corresponding discovery resource area from the point of view ofreception.

In the example of FIG. 25, the discovery resource area A 2503 and thediscovery resource area B 2505 may be allocated to UEs placed in thecenters of cells. Furthermore, the discovery resource area C 2507 may beallocated to UE placed in a cell edge area and UE placed at the edgearea of a neighbor cell.

If UEs sense discovery messages using methods, such as those of FIGS. 24and 25, and differently configures their discovery message transmissionsections for each subband/slot according to frequency/time, the numberof D2D UEs capable of receiving discovery messages may look likereducing because the time taken to sense a discovery message is reduced.If UEs which have to sense all discovery messages are divided into 3regions (i.e., 3 subbands/sections), however, it may be determined thatthe number of UEs which have to actually sense discovery messages hasbeen reduced to ⅓ on the assumption that the UEs have been uniformlydistributed. Furthermore, the frequency/time have been reduced to ⅓unlike in an existing hopping pattern, but small UEs whosefrequency/time have been reduced to ⅓ may perform D2D discovery in apredetermined frequency/time based on a subband/slot within the reducedfrequency/time if they perform transmission according to a hoppingpattern based on the time/frequency using resources three times existingresources.

FIG. 26 shows an example in which discovery resource areas aredistinctly configured according to an embodiment of the presentinvention.

In FIG. 26, small squares indicate discovery resources now used by otherUEs, and different patterns of the squares indicate that the discoveryresources are used by different UEs.

In FIG. 26, a discovery resource pool 2601 is configured to include 44RB pairs in a frequency domain and configured to include 64 subframes ina time domain. Furthermore, it is assumed that the discovery resourcepool 2601 is divided into discovery resource areas based on the RSRPvalues of RSs received by UEs. Furthermore, the entire range of RSRP is−60 dbm to 60 dbm in a corresponding cell.

FIG. 26 illustrates that the number of UEs is 12 in a cell and eachdiscovery resource area has been divided into 12 frequency-time domainsfor each UE.

Referring to FIG. 26, a specific RSRP value (or RSRP range) may bemapped to each of discovery resource areas 2603 to 2625 divided in thein the time and frequency domains. In other words, the entire range ofRSRP of −60 dbm˜60 dbm is divided at a 10 dbm interval, and the RSRPranges divided at the 10 dbm interval may be mapped to the discoveryresource areas 2603 to 2625. That is, in FIGS. 24 and 25, the discoveryresource area has been allocated in the frequency or time domain basedon an RSRP value measured by UE. In contrast, in the example of FIG. 26,an RSRP range and each discovery resource area are subdivided in thefrequency and time domains and mapped. For example, if the RSRPmeasurement value of UE1 belongs to −60 dbm˜−50 dbm, the UE1 may sense adiscovery message resource within the discovery resource area A 2603 andthen select a discovery resource for sending its discovery message.Furthermore, if the RSRP measurement value of UE2 belongs to −50 dbm˜−40dbm, the UE2 may sense a discovery message resource within the discoveryresource area B 2605 and then select a discovery resource for sensingits discovery message.

In FIG. 26, the discovery resource areas have been illustrated as beingcontiguously configured in the time and frequency domains, but they maybe discontiguously (e.g., based on a discontiguous RB group and/or adiscontiguous subframe group) configured in the time and/or frequencydomains. Furthermore, in FIG. 26, the discovery resource areas have beenillustrated as not overlap, but the present invention is not limitedthereto. For example, adjacent discovery resource areas may overlap.

Furthermore, even in the method of dividing the entire discoveryresource pool into discovery resource areas in the time and frequencydomains based on RSRP values measured by UEs, the UEs may be grouped bytaken into consideration cell IDs.

For example, groups may be formed in such a manner that a cell 1 isclassified as a group 1 (e.g., the discovery resource area A 2603 to thediscovery resource area H 2617) if the cell 1 has maximum RSRP and acell 2 is classified as a group 2 (e.g., the discovery resource area I2619 to the discovery resource area L 2625) if the cell 2 has maximumRSRP. Discovery resource areas may be determined based on RSRP measuredby UE within each of the cells 1 and 2.

Furthermore, groups may be formed in such a manner that a cell isclassified as a group A (e.g., the discovery resource area A 2603 to thediscovery resource area H 2617) if RSRP of the cell is a predeterminedthreshold or more and a cell is classified as a group B (e.g., thediscovery resource area I 2619 to the discovery resource area L 2625) ifRSRP of the cell is less than the predetermined threshold. Discoveryresource areas may be determined based on RSRP measured by UE withineach of the cells 1 and 2.

Furthermore, UE placed at the edge of a neighbor cell may also beincluded by taking into consideration discovery between multiple cells.For example, the discovery resource area A 2603 to the discoveryresource area H 2617 may be allocated to UE placed in the center of eachcell. Furthermore, the discovery resource area I 2619 to the discoveryresource area L 2625 may be allocated to UE placed in a cell edge areaand UE placed at the edge area of a neighbor cell.

Unlike in the aforementioned method, discovery resource areas may beconfigured by dividing the entire discovery resource pool in a frequencydomain based on an RSRP value measured by UE, and a discovery resourcemay be selected by dividing a discovery resource area into subframeconfiguration sets allocated to each UE group in a time domain. Forexample, a UE group 1 may use a first subframe configuration set inorder to select a discovery resource, and a UE group 2 may use a secondsubframe configuration set in order to select a discovery resource. Thatis, UE selects a discovery resource within a discovery resource areadetermined based on RSRP measured by the UE, but may select thediscovery resource randomly or based on a specific probability within asubframe configuration set allocated by the eNB. In this case, thesubframe configuration set may include a plurality of contiguous ordiscontiguous subframes.

More specifically, an eNB or UE may group adjacent UEs and a specificsubframe configuration set may be used for each UE group so that UEsbelonging to RSRP having the same or similar range receive or senddiscovery messages in the same subframe intensively. For example, an eNBmay notify adjacent UEs (i.e., a UE group) of specific subframeconfiguration set information through RRC signaling or a physical layerchannel (e.g., a PUCCH or PUSCH) based on RRM measurement information orCSI received from the UEs. Furthermore, UEs may notify surrounding UEsof their subframe configuration set information through a D2Dsynchronization signal or discovery message. Alternatively, grouping maybe performed based on a UE ID, and a different subframe configurationset may be allocated to each group.

Furthermore, UE may be made to automatically recognize a subframeconfiguration set, used by the UE, based on RSRP. What a discoverymessage has to be transmitted or received in which discovery resource(e.g., a subframe or subframe group) may be determined with reference toa measured value, such as RSRP owned by UE through measurement, and anRSRP classification reference within a cell because the measured value.

Since two or more UEs are able to discover each other through adiscovery procedure, each UE may randomly select a subframe in which adiscovery message is transmitted in its subframe configurationset/group. That is, each UE may select an operation for sending whichsubframe in a given subframe configuration set and not sending whichsubframe in the given subframe configuration set randomly or based on aspecific probability. In contrast, UE which detects a discovery messagemay monitor all such subframe configuration sets and efficiently detectproximity UE.

Meanwhile, the discovery resource area configured using the methodsdescribed with reference to FIGS. 24 to 26 may be changed for eachdiscovery resource pool or for each discovery cycle as described above.

Furthermore, the discovery resource area may be variably changeddepending on a service used by a user or the setting (or input) of auser. For example, in a D2D discovery process, the range in which UE tobe discovered is discovered may be various for each UE. If a servicesuitable for discovering UE in a wide range is used, adjacent UEs are tobe discovered in a wide range, or a larger number of UEs are to bediscovered, the range of a discovery resource area may be set larger,sensing may be performed within the discovery resource area that is setlarger, and a discovery resource may be selected. In contrast, if anirrelevant service is used although UE is discovered in a narrow range,adjacent UEs are to be discovered in a narrow range, or a small numberof UEs are to be discovered, the range of a discovery resource area maybe set small, sensing may be performed within the discovery resourcearea that is set small, and a discovery resource may be selected.

In other words, a discovery range and/or the number of discoverabledevices may influence such parameters. Such a demand may be generated inservices for public safety or commercial purposes. That is, a discoveryrange and/or the number of discoverable devices may be differentdepending on which service (or application) is used.

Furthermore, a user may directly input a discovery range and/or thenumber of discoverable devices or select (or control) a discovery rangeand/or the number of discoverable devices through a switch manipulation.In other words, in order to change the range in which many users are tobe discovered in a narrow area or small users are to be discovered in awide area and to change the number of discoverable devices, a user maydirectly set the parameters. Simply, a user may directly set theparameters using an external switch, such as a dip switch.

FIGS. 24 to 26 have illustrated the method of grouping UEs based on theresults of cell measurement (e.g., RLM, RRM, and CSI) using RSstransmitted by an eNB and mapping a discovery resource area for each UE.However, the present invention is not limited to an RS transmitted by aneNB, and a discovery resource area to be used may be determined by thesignal quality and intensity of a signal transmitted by another UE. Thisis described in more detail below with reference to FIG. 27.

FIG. 27 is a diagram illustrating a method for determining a discoveryresource area based on a signal transmitted by UE according to anembodiment of the present invention.

Referring to FIG. 27(a), a network sets specific UEs as a kind ofreference UE. In FIG. 27, it is assumed that UE A, UE B, and UE C havebeen set as reference UE.

In this case, UEs that are placed geographically distant may be set asreference UE. Furthermore, if discovery between cells is taken intoconsideration as described above, a discovery resource area may also beconfigured in the same discovery pool with respect to UE placed at theedge area of a neighbor cell. Accordingly, reference UEs are not relatedto whether they belong to a specific cell. That is, all of the UE A, theUE B, and the UE C may be placed in the same cell coverage or may beplaced in different cell coverage.

Furthermore, as in FIG. 27(b), the reference UEs (i.e., the UE A, the UEB, and the UE C) may be associated with respective groups, and discoveryresource areas mapped to the respective groups may be configured. Thatis, the UE A may be mapped to a discovery resource area A 2703, the UE Bmay be mapped to a discovery resource area B 2705, and the UE C may bemapped to a discovery resource area C 2707. In this case, each discoveryresource area mapped to the reference UE may be segmented by combiningone or more of a frequency domain, a time domain, and a spatial domainas described above. Furthermore, the discovery resource area mapped tothe reference UE may be segmented by taking into consideration a UE IDor a cell ID.

In this case, regarding the remaining UEs other than the reference UE, adiscovery resource area to be used may be selected based on the qualityand intensity of a signal received by the reference UE. For example, adiscovery resource area associated with reference UE from which thestrongest signal is received or a signal having the best quality isreceived may be used. In the example of FIG. 27, UE 1 receives signalsfrom the UE A, the UE B, and the UE C, respectively, determines a signalhaving the highest reception signal intensity or a signal having thebest reception signal quality, and selects a discovery resource areaassociated with UE which has sent the corresponding signal.

Furthermore, the UE 1 senses a discovery message in the selecteddiscovery resource area, searches the sensed resources for resourceshaving a low energy level, and randomly selects a discovery resourcewithin a specific range (e.g., low x % (x=a specific integer, 5, 7, 10,. . . ) in the retrieved resources.

In order to determine a discovery resource area to be used, a discoverysignal transmitted by reference UE may be used. If reference UE sends asynchronization signal for discovery, the synchronization signal may beused to determine a discovery resource area to be used.

As described above, if infrastructure is supported using the method fordetermining a discovery resource area using an RS, which is proposed byan embodiment of the present invention, a discovery procedure using anexisting dispersive method can be efficiently improved. Furthermore,what UE measures RSRP using RS information is a technology nowimplemented in LTE UEs. If such a technology is used, UE can beefficiently discovered based on surrounding UEs in a D2D discoverywithout proposing a change of the LTE standard or a new signal orprotocol. Furthermore, consumed energy can be reduced by reducing thetime taken for UE to perform sensing for discovery. Furthermore,processing overhead for the sensing of UE and for discovery resourceselection can be reduced compared to existing discovery methods becausea sensed frequency section is reduced and a discovery resource isselected. Furthermore, various sensing configurations and resourceselection are made possible based on a required service or rangeaccording to various requirements which may be taken into considerationin a D2D discovery step.

In the aforementioned description of the present invention, a method forlimiting a discovery resource area to a time domain and/or frequencydomain and performing a sensing or transmission operation has beenmostly illustrated, but this is for convenience of description and thepresent invention is not limited thereto. As described above, adiscovery resource area may be divided even in a spatial domain in thesame manner using the method of configuring a discovery resource area ina time domain or frequency domain. Furthermore, as in the method ofcombining time and frequency domains and dividing a discovery resourcearea, a spatial domain may be combined with time and frequency domainsand a discovery resource area may be divided. Furthermore, other regions(e.g., a UE ID and/or a cell ID) may be combined other than the time,frequency, and spatial domains, and an operation according to anembodiment of the present invention may be performed.

Furthermore, in the aforementioned description of the present invention,the method of determining, by each UE, that it has to send a discoverymessage in which discovery resource area based on RSRP has been mostlyillustrated, but this is for convenience of description and the presentinvention is not limited thereto. As described above, various values inaddition to RSRP may be used as parameters for determining the discoveryresource area of UE. For example, RLM, RSRQ, RSSI, CSI, and pathloss mayalso be used as parameters for determining the discovery resource areaof UE. That is, factors used between UE and an eNB, which may be used toestimate the position or proximity of UE, may be used as parameters fordetermining a discovery resource area for the sensing and transmissionof a discovery resource according to an embodiment of the presentinvention. Furthermore, one or more factors may be combined and used asparameters for determining a discovery resource area. For example, adiscovery resource area may be determined by combining and using RSRPand RSRQ or by taking into consideration RSRP, RSRQ, and pathlosstogether.

Delayed Response-Based D2D Search Method

Recently, disaster communication services and technology standardizationusing a 3GPP LTE/LTE-A mobile communication network have been activelyconducted. In 3GPP, a group communication service utilizing aproximity-based communication technology and a discovery serviceutilizing a D2D discovery signal/message to transfer an emergency rescuerequest signal are mentioned as representative use cases of disastercommunication and relevant services and technical standards have beendiscussed.

Disaster communication include all the wide range of problems such as apublic warning system through disaster recognition, information exchangebetween UEs in a disaster area, infrastructure network access, and thelike.

The present invention proposes a technique of effectively and promptlyaccessing an infrastructure network by utilizing an inter-UE directcommunication technology in a state in which the entirety or a portionof a communication infrastructure cannot be used in a disaster situation(for example, an out-of-coverage or partial network coverage scenario).That is, the present invention intends to realize information exchangebetween UEs and infrastructure network access in a disaster area inorder for UEs of the disaster area to provide information regarding aspecific disaster situation and information required for prompt rescue.

Hereinafter, for UE discovery, a discovery signal will be assumed anddescribed, but the present invention is not limited thereto. That is, asynchronization signal, a beacon signal, a reference signal, a D2Ddirect communication signal, and the like, may also be used.

FIG. 28 is a view illustrating a situation in which UEs in a disasterarea access an infrastructure network according to an embodiment of thepresent invention.

Referring to FIG. 28, an eNB-PS (enhanced-Node B of Public SafetyNetwork) represents a disrupted base station (BS) in a disaster area,and an eNB-NPS (eNB of Non-Public Safety Network) represents a neighborBS which has recognized a situation in which the eNB-PS does notnormally operate.

When a disaster situation occurs so the eNB is disrupted, eNBs (i.e.,eNB-NPS 1 and eNB-NPS 2) of adjacent cells detect a correspondingsituation, allocates resource (e.g., a resource pool) for transmitting aD2D discovery signal to UEs appropriate for UE discovery among UEs thatbelong to the cells thereof and subsequently permits (or commands) theUEs to perform UE discovery on UEs of the disaster area. Resource fortransmitting the D2D discovery signal may be allocated in advance or inreal time (i.e., when performing discovery is permitted).

UEs outside of coverage may detect (i.e., receive) a discovery signaltransmitted from UEs within coverage, and receive information (e.g., aUE ID (identifier)) of adjacent UEs available for D2D communication andinformation regarding a D2D signal transmission resource through thereceived discovery signal.

In the sequential processes, a D2D transmission environment maydeteriorate due to resource conflict among a plurality of D2D UEspresent outside of coverage, in the boundary of coverage, and withincoverage and restrictions for protecting a wide area network (WAN) UEwithin coverage, and thus, a UE recognition method for minimizingresource conflict among UEs and minimizing battery consumption isrequired.

A plurality of disaster area UEs may discover a neighbor BS and attemptaccess or a UE unable to discover a neighbor BS may search for a signalof a neighbor D2D UE and so as to be connected to a D2D relay UE withincoverage through hopping using various D2D relay functions. In thisprocess, indiscriminate signal transmissions may be made to causeresource conflict between D2D UEs or between cellular resources andineffective use of resource. Thus, it is desirable to optimize a systemoperation by minimizing signals unnecessarily exchanged in terms ofentire UEs or individual UEs.

FIG. 29 is a view illustrating a UE discovery method according to anembodiment of the present invention.

In the present invention, a model in which a resource pool required fortransmitting a discovery signal and a D2D signal is received from a UEthat belongs to an eNB-NPS (eNB of Non-Public Safety Network), aneighbor BS which has detected a situation in which an eNB-PS(enhanced-Node B of Public Safety Network), a disrupted BS of a disasterarea, does not normally operate is considered.

It is anticipated that indiscriminate signal transmissions may be madewhile UEs in the disaster area receive a discovery signal transmitted bya UE of an adjacent cell and respond thereto, which may inevitably causeresource conflict and ineffective use of resource.

Thus, the present invention aims to reduce resource conflict byminimizing unnecessary signal transmission of UEs by utilizing D2Dsignal transmission and discovery method of a response delay-based D2DUE.

In the method proposed in the present invention, a UE that transmits adiscovery signal transmits a signal only once during a discovery periodand maintains a reception mode during the other remaining time.

UEs, which receive the discovery signal, wait for a predetermined periodof time and transmit a response signal on the basis of a magnitude ofreception SINR (Signal-to-Interference plus Noise Ratio) (or an SNR(Signal-to-Noise Ratio), an RSRP (Reference Signal Receive Power), anRSRQ (Reference Signal Received Quality), or an RSSI (Received SignalStrength Indicator), etc.) of each UE, instead of responding at apreviously designated fixed time.

That is, after the discovery signal is received, a response delay timeis determined according to a reception SINR, and when the response delaytime terminates, a response signal is transmitted. Here, the responsedelay time may be determined to be in inverse proportion to thereception SINR.

For example, as the SINR is higher, a corresponding UE is highly likelyto be positioned in the proximity of the discovery signal transmissionterminal so a short response delay time is determined for the UE, and asthe SINR is lower, a corresponding UE is highly likely to be positionedto be distant from the discovery signal transmission terminal so a longresponse delay time may be determined for the UE.

Equation 16 expresses an example of determining a response delay time.

$\begin{matrix}{{{Response\_ delay} = {\frac{\beta_{D}}{\beta_{D} + {SNR}} \cdot {discovery\_ period}}};} & \lbrack {{Equation}\mspace{14mu} 16} \rbrack\end{matrix}$

In Equation 16, β_(D) denotes a D2D target SINR/SNR. The target SINR/SNRvalue may be set in advance.

Here, the discovery signal includes information required for discoverysuch as a

UE ID and/or a discovery period, and the response signal includes a UEID. Each UE may identify neighbor UEs available for D2D communicationwith each UE through a UE ID transmitted and included in the receiveddiscovery signal or response signal.

FIG. 30 is a view illustrating a D2D UE discovery method according to anembodiment of the present invention.

In FIG. 30, in order to clarify features of a delayed response, anabsolute and relative propagation delay time during which a transmissionsignal (i.e., a discovery signal or a response signal) is transmitted ispartially enlarged and illustrated. That is, both propagation delay andresponse delay are illustrated in the same drawing, a propagation delayrelative time interval and a delay response relative time in accordancewith an SINR should be understood by applying different scales.

In the present invention, a synchronous D2D terminal discovery isassumed. That is, every UE transmits a discovery signal and alsoreceives a discovery signal transmitted from an adjacent UE. Also, it isassumed that an eNB of a cell adjacent to a disaster area may detect adisaster situation through back haul.

A proposed response delay-based terminal discovery procedure will bedescribed on the basis of the example of FIG. 30.

1) An eNB of a cell, which is adjacent to a disaster area and hasdetected a disaster situation through back haul, selects a UE1-NPS, a UEadjacent to the disaster situation and appropriate for relaying, amongUEs that belong to the corresponding cell, allocates a resource poolrequired for transmitting a D2D discovery signal to the UE, and enablesthe UE to perform UE discovery.

Here, the eNB may implicitly instruct the UE to perform UE discovery byallocating a resource pool, and may explicitly instruct through anindicator for performing UE discovery together with a resource pool.

2) Allocated the resource pool from the eNB, the UE1-NPS transmits adiscovery signal 3001 toward the UEs in the disaster area andsubsequently maintains a reception mode during a remaining time until adiscovery period 3006 terminates.

Also, when the UEs (i.e., UE2-PS, UE3-PS, UE4-PS) positioned in thedisaster area are disconnected from the eNB-PS to which they belong dueto the disaster situation, the UEs maintain a reception mode in order toreceive a discovery signal from the UE positioned in an adjacent cell.

Here, the discovery signal 3001 includes a UE ID.

Also, the discovery signal 3001 may include discovery period 3006information.

In a case in which the discovery period 3006 is not synchronized in eachcell, the discovery signal 3001 may include discovery period 3006information to adjust synchronization of the discovery period 3006between UEs that belong to the disaster area cell and UEs that belong toa cell adjacent to the disaster area.

Also, the discovery signal 3001 may not include the discovery period3006 information. When the discovery period 3006 is synchronized in eachcell, the UEs may receive the discovery period 3006 information from theBSs to which they belong. Here, the discovery period 3006 may betransmitted through system information (e.g., a master information block(MIB) or a system information block (SIB)).

3) Rather than immediately responding to the discovery signal, theUE2-PS, UE3-PS, and UE4-PS of the disaster area have a different(variable) response delay 3007 value determined according to a magnitudeof a reception SINR and wait for a corresponding response delay 3007time. That is, UEs having a high reception SINR have a relatively shortresponse delay 3007, compared with UEs having a low SINR.

Here, in order to determine the response delay 3007, parameters such asa strength of a signal from the UE (i.e., the UE1-NPS) which hastransmitted the discovery signal, signal quality, path loss, and thelike, may be used. Here, in a case in which the UE1-NPS transmits areference signal to determine the response delay 3007, strength orquality of the reference signal may be used as a reference thereof.

4) When the determined response delay 3007 time terminates, the UEs(i.e., UE2-PS, UE3-PS, and UE4-PS) of the disaster area transmits aresponse signal 3002 regarding the discovery signal received from theUE1-NPS.

In FIG. 30, since the UE2-PS has a relatively high reception SINR, ithas a short response delay 3007, compared with other UEs (i.e., theUE2-PS and the UE3-PS), and thus, the UE2-PS first responds to thediscovery signal received from the UE1-NPS. Also, the UE1-NPS detectsthe corresponding response signal 3002 to recognize presence of theUE2-PS.

When the response delay 3007 of each of the UE2-PS and the UE3-PSterminates, the UE2-PS and the UE3-PS sequentially transmit the responsesignal 3002 to the UE1-NPS, and upon detecting the correspondingresponse signal 3002, the UE1-NPS successfully recognizes presence ofthe UE2-PS and the UE3-PS and the discovery period 3006 terminates.

Here, if the determined response delay 3007 is longer than the discoverperiod 3006, the discovery period 3006 terminates in a state in whichthe response signal 3002 is not transmitted yet, and thus, the UE1-NPScannot recognize presence of a corresponding UE. In FIG. 30, since arelatively long response delay 3007 of the UE5-PS is determined, it isnot discovered by the UE1-NPS.

5) Having successfully finished UE discovery, the UE1-NPS selects a UEto which the discovery signal is to be transmitted during a nextdiscovery period, and forwards a resource pool for transmitting thediscovery signal thereto.

Here, the UE1-NPS may select a UE to which the discovery signal is to betransmitted in consideration of the three schemes as follows.

Scheme 1) The UE1-NPS may select a UE which has the shortest responsedelay 3007 and has first transmitted a response signal 3002 with respectto the discovery signal 3001. This will be described with reference toFIG. 31.

FIG. 31 is a view illustrating a UE discovery method according to anembodiment of the present invention.

Referring to FIGS. 30 and 31, since the UE2-PS has a relatively highSINR, it has a relatively short response delay 3007, compared with otherUEs (i.e., the UE3-PS and the UE4-PS), and thus, the UE2-PS firsttransmits a response signal 3002 in response to the discovery signalfrom the UE1-NPS. The selects the UE2-PS which has first transmitted theresponse signal 3002, forwards a resource pool, and enables the UE2-PSto perform UE discovery during a next discovery period.

The UE1-NPS may transmit information regarding a subframe pool and/or aresource block pool that belongs to the resource pool, as resource poolinformation, to the UE2-PS. The subframe pool and/or the resource blockpool may be indicated by a bitmap or a start/end subframe/resource blockindex.

Scheme 2) The UE1-NPS may select a UE which has the longest responsedelay 3007 and responds the latest. This will be described withreference to FIG. 32.

FIG. 32 is a view illustrating a UE discovery method according to anembodiment of the present invention.

Referring to FIGS. 30 and 32, since the UE4-PS has a relatively lowreception SINR, compared with other UEs (i.e., the UE2-PS and theUE3-PS) which have transmitted a response signal, the UE4-PS has arelatively short response delay 3007 and transmits the response signal3002 the latest with respect to the discovery signal of the UE1-NPS,compared with other UEs. The UE1-NPS selects the UE4-PS which hastransmitted the response signal 3002 the latest, forwards a resourcepool, and enables the UE4-PS to perform UE discovery during a nextdiscovery period.

Scheme 3) The UE1-NPS randomly selects a certain UE among the UEs whichhave transmitted the response signal 3002 with respect to the discoverysignal 3001.

It is assumed that the UE1-NPS randomly selects the UE3-PS and transmitsresource pool information.

The UE1-NPS selects an arbitrary UE among the UE2-PS, the UE3-PS, andthe UE4-PS which have transmitted the response signal 3002, forwards aresource pool thereto, and enables the selected UE to perform UEdiscovery during a next discovery period.

6) The UE of the disaster area, which has received the resource pool,randomly selects an available resource from the resource pool andperforms UE discovery.

That is, in the example illustrated in FIG. 31, the UE2-PS, which hasreceived the resource pool information from the UE1-NPS, transmits thediscovery signal 3003 from a resource randomly selected from theresource pool toward neighbor UEs. Also, in the foregoing example ofFIG. 32, the UE4-PS, which has received the resource pool informationfrom the UE1-NPS, transmits a discovery signal 3004 from a resourcerandomly selected from the resource pool toward neighbor UEs. Also, therandomly selected UE3-PS in the foregoing example receives the resourcepool information from the UE1-NPS and transmits a discovery signal 3005from a resource randomly selected from the resource pool toward neighborUEs.

The UEs, which have recognized the presence of the neighbor UEs, doesnot respond to a discovery signal any longer, and only the terminalsthat first receive the discovery signal responds thereto. The UEdiscovery proposed in the present invention is repeatedly performeduntil there are no more UEs to which the discovery signal is to betransmitted, among the UEs of the disaster area.

A scheme in which the UE1-NPS selects a UE for performing UE discoveryduring a next discovery period and a scheme in which the selected UEselects a UE for performing UE discovery during a next discovery periodmay be independently determined for each UE. For example, the UE1-NPSselects a UE which has first transmitted a response signal, as a UEwhich is to perform UE discovery, and the selected UE may select anarbitrary UE as a UE for performing UE discovery during a next discoveryperiod.

Meanwhile, the UE1-NPS may not select a UE for performing UE discoveryduring a next discovery period, and a UE for performing UE discoveryduring a next discovery period may be implicitly selected.

In detail, in the example of FIG. 30, since the UE2-PS has the highestSINR, it has a short response delay, compared with the UE3-PS and theUE4-PS, and thus, the UE2-PS first responds to the discovery signal fromthe UE1-NPS. Here, the UE3-PS and the UE4-PS which have been maintainedin the reception mode listen to a response signal that the UE2-PS hastransmitted to the UE1-NPS.

The UE3-PS and the UE4-PS abandon responding to the discovery signalfrom the UE1-NPS and transmit a response signal to the UE2-PS instead.The UE1-NPS, which has been maintained in the reception mode after ithad received the response signal from the UE2-PS, listens to theresponse signal that the UE3-PS and the UE4-PS have transmitted to theUE2-PS, and recognizes presence of the UE3-PS and the UE4-PS.

Accordingly, the UE1-NPS successfully discovers the UE2-PS, the UE3-PS,and the UE4-PS, and the UE2-PS recognizes presence of the UE1-NPS, theUE3-PS, and the UE4-PS and finishes the UE discovery process of thediscovery period.

Since the UE1-NPS has successfully terminated the UE discovery, theUE2-PS which has successfully discovered the neighbor UEs other than theUE1-NPS performs UE discovery at a next discover period. That is, theUE, which has transmitted the response signal fastest performs UEdiscovery at a next discovery period.

Since the discovery signal and the response signal include a UE ID, theUE1-NPS, the UE3-PS, and the UE4-PS, among the UEs which have receivedthe discovery signal from the UE2-PS, already recognize presence of theUE2-PS, so they do not transmit a response signal any longer, and UEs ofthe disaster area other than the UE5-PS that first receives thediscovery signal, discover UEs available for D2D communication nearby.Repeating this process, UE discovery is continuously performed until theinnermost UE of the cell of the disaster area is discovered, to form amulti-hop link for accessing an external infrastructure network.

In the UE discovery method proposed in the present invention, it isassumed that UE discovery and D2D direct communication use the sameresource. Thus, information of a UE available for D2D communicationnearby and resource information to be used for communicating with thecorresponding terminal may be provided together.

Thus, advantageously, there is no need to separately allocate resourcerequired for transmission of a D2D signal of disaster area terminals.

FIG. 33 is a view illustrating a method for allocating resourcesimultaneously with UE discovery according to an embodiment of thepresent invention.

Referring to FIG. 33, it is assumed that a resource pool allocated foran eNB of a cell which is adjacent to a disaster area and has detected adisaster situation to discover UEs positioned in the disaster area isthe UE1-NPS to UEn-PS.

Also, it is assumed that the UE1-NPS that belongs to the cell of the eNBof the cell which is adjacent to the disaster area and has detected thedisaster situation transmits a discovery signal and UEs from whichresponse signals thereto are received so as to be discovered are theUE2-PS, the UE3-PS, and the UE4-PS.

Also, it is assumed that the UE1-NPS that belongs to the cell of the eNBof the cell which is adjacent to the disaster area and has detected thedisaster situation selects the UE2-PS as a UE for discovering neighborUEs at a next discovery period and it is assumed that the UE2-PS selectsthe UE5-PS as a UE for discovering neighbor UEs at a next discoveryperiod.

The UE1-NPS, which belongs to the cell of the eNB of the cell which isadjacent to the disaster area and has detected the disaster situation,selects the UE1-NPS resource RB1 3301 randomly selected from theresource pool and transmits a discovery message. Also, the UE1-NPS mayequally use the resource 3301 used for transmitting the discoverymessage in order to perform D2D direct communication with the UE2-PS,the UE3-PS, and the UE4-PS discovered by the UE1-NPS. That is, thecorresponding frequency region (e.g., RB) may be used by the UE1-NPS forD2D direct communication within the same discovery period.

Also, the UE2-PS and the UE5-PS selected by the UE1-NPS to discover aneighbor UE may use resource (i.e., RB1 3302 and RB2 3303) used by theUE2-PS and the UE5-PS to transmit the discovery signal, for D2D directcommunication.

Thus, for example, the UE2-PS receives signals transmitted from theUE1-NPS and the UE5-PS by using the RB1 3301 and the RB3 3303. Also, theUE4-PS, which only receives a discover signal, exchanges informationwith the UE1-NPS through D2D direct communication by using the RB 13301, which has been used by the UE1-NPS, an adjacent UE available forD2D direct communication, to transmit the discovery signal.

FIG. 34 is a view illustrating a UE discovery method according to anembodiment of the present invention.

In FIG. 34, it is assumed that the eNB of the cell which is adjacent tothe disaster area and has detected the disaster situation through backhaul selects a UE1 for performing UE discovery because the UE1 isadjacent to the disaster situation and appropriate for relaying, amongUEs that belong to the corresponding cell. Also, it is assumed that theUEs of the disaster area are UE2 to UEn.

Referring to FIG. 34, the UE1 transmits a discovery signal toward theUEs (i.e., the UE2 to UEn) of the disaster area (S3401).

The UE1 may be allocated a resource pool required for transmission of aD2D signal from the BS and transmit a D2D discovery signal from aresource randomly selected from the resource pool.

Here, the discovery signal may include a UE ID and/or discovery periodinformation.

After transmitting the discovery signal, the UE1 is switched to areception mode and maintains the reception mode for a remaining periodof time until the discovery period terminates.

Meanwhile, when the UEs (i.e., the UE2 to UEn) positioned in thedisaster area are disconnected from the eNB to which they belong, theUEs maintain a reception mode in order to receive a discovery signalfrom the UE positioned in the adjacent cell.

Upon receiving the discovery signal from the UE1, the UE2 to UEndetermine a response delay time on the basis of a reception SINR(S3402).

Here, the reception SINR may be derived using the received discoverysignal, and here, in a case in which the UE1 transmits a referencesignal, the reception SINR may be derived on the basis of the referencesignal.

Also, UEs having a high reception SINR has a relatively short responsedelay, compared with UEs having a low SINR. That is, the response delaytime is determined to be in inverse proportion to the reception SINR.

The UE2 to UEn wait for the corresponding response delay time.

When the calculated response delay terminates, the UE2 to UEn transmit aresponse signal (S3403). That is, each of the UEs independently has acalculated response delay time, and when the response delay time thereofterminates, each of the UEs transmits a response signal.

After transmitting the response signal, the UE2 to UEn are switched to areception mode and maintain the reception mode for a remaining period oftime until the discovery period terminates.

Upon receiving the response signals from the UE2 to UEn, the UE1 selectsa UE for performing a UE discovery process at a next discovery period,among the UEs which have transmitted the response signals (S3404). Thatis, the UE1 selects a UE for transmitting a discovery signal at a nextdiscovery period.

Here, the UE1 may select a UE for performing the UE discovery process ata next discovery period by using any one of the three schemes describedabove. That is, the UE1 may select a UE which has transmitted a responsesignal first, a UE which has transmitted the response signal the latest,or an arbitrary UE

In FIG. 34, it is assumed that the UE1 selects the UE2 as a UE forperforming a UE discovery process at a next discovery period.

The UE1 transmits resource pool information to the UE2 (S3405).

Thereafter, the UE (i.e., the UE2) of the disaster area which hasreceived the resource pool randomly selects an available resource fromthe resource pool and performs UE discovery. The UE discovery process isrepeatedly performed until every UE positioned in the disaster area isdiscovered

FIG. 35 is a view illustrating a difference between an existing UEdiscovery method and a UE discovery method proposed in the presentinvention.

FIG. 35(a) is a view illustrating an existing UE discovery scheme, andFIG. 35(b 0 is a view illustrating a UE discovery scheme proposed in thepresent invention.

Referring to FIG. 35, compared with the existing UE discovery as ascheme of responding only to a discovery signal, in the UE discoverymethod proposed in the present invention, the UEs, which have receivedthe discovery signal, are on standby in a reception mode for apredetermined period of time on the basis of an SNIR thereof, or thelike, and sequentially transmit a response signal, thus obtaining aneffect of reducing a resource conflict between the UEs.

Also, since a UE listens to a response signal transmitted by another UEin the reception mode and transmits a respond signal, whereby a link maybe additionally formed between the UE2 and the UE3 and between the UE2and the UE4 as illustrated in FIG. 35(b), compared with the existing UEdiscovery.

The UE discovery performance of the D2D UE discovery scheme based on aresponse delay and the infrastructure access performance proposed in thepresent invention were verified through a simulation in an environmentas illustrated in Table 6.

TABLE 6 Parameter Value ISD (Inter-Site Distance) 500 m Number of eNBs 1for NPS (100% enabled) 1 for PS (0% enabled) Number of UEs 75 UEs incase of NPS, and 25 UEs in case of PS UE distribution NPS: Uniform(entire cells) PS: Uniform (⅙ of cell adjacent to NPS) Minimum distancebetween UEs 20 m Path loss model (D2D) 148.1 + 40log10(d [km]) Shadowfading 7 dB log-normal Thermal noise PSD (power −174 dBm/Hz spectraldensity)) Noise figure at all UEs 9 dB Channel bandwidth 180 kHzResource allocation Randomly 1 PRB per UE UE transmission power 23 dBmTarget SINR 10 dB Discovery period 8 s Beacon (discovery signal) 0.5 mstransmission/reception time

In order to verify the discovery performance of the UE discovery schemebased on response delay proposed in the present invention under theenvironment of Table 6, the number of transmissions of the discoverysignal during the entire discovery period until the UE discoveryterminated and the number of successfully discovering the innermost UEof a disaster area in which an eNB was disrupted were derived.

FIG. 36 is a view illustrating results of a simulation of UE discoveryperformance of response delay-based UE discovery according to anembodiment of the present invention.

In FIG. 36, the horizontal axis represents three schemes (scheme 1,scheme 2, and scheme 3) proposed in the present invention, and thevertical axis represents the number (the number of hops or the number ofdiscovered UEs).

Performances of three different cases of the schemes described abovewere compared (the schemes were (1) Scheme 1: UE discovery was performedby selecting a UE having the shortest response delay, (2) Scheme 2: UEdiscovery was performed by selecting a UE having the longest responsedelay, and (3) Scheme 3: UE discovery was performed by selecting acertain UE among UEs which transmitted a response).

In the simulation, the number of transmissions of a discovery signal(the number of hops) (the average hop number 3601) during the entirediscovery period until UE discovery terminated and the number ofsuccessfully discovering the innermost UE of the disaster area in whichan eNB was disrupted (average number of innermost UE discovered (×100)3602) were derived in each scheme.

The results derived from the simulation are average values obtained byexecuting the proposed discovery scheme 1000 times in different UE dropenvironments.

Referring to FIG. 36, it can be seen that Scheme 2 in which UE discoverycontinued for a relatively long period of time and the number ofsuccessfully discovering the innermost UE of the disaster area cell waslarge exhibits the best performance in terms of network coverage.

Also, in order to verify infrastructure access performance of theproposed scheme, an experiment regarding whether UEs of the disasterarea discovered during the entire discovery period formed abi-directional link satisfying a threshold SINR value was conducted.

FIG. 37 is a view illustrating results of a simulation of infrastructureaccess performance of a response delay-based UE discovery methodaccording to an embodiment of the present invention.

In FIG. 37, the horizontal axis represents the three schemes (Scheme 1,Scheme 2, and Scheme 3) proposed in the present invention, and thevertical axis represents the number of UEs.

Performances of three different cases in which UE discovery wasperformed by selecting any one of Scheme 1, Scheme 2, and Scheme 3described above were compared.

In order for terminals of the disaster area to successfully access anadjacent infrastructure, (1) SINRs at the time when UEs, which havetransmitted discovery signals playing a pivot role for infrastructureaccess, receive the mutual discovery signals should satisfy a thresholdvalue, and (2) an SINR of a terminal which has transmitted a discoverysignal when a UE, which only receives a discovery signal, transmits aresponse signal should satisfy a threshold value.

In the simulation, the average number of discovered UEs 3701 and theaverage number of network access UEs 3702 of each scheme were derived.

The results derived in the simulation are average values obtained byexecuting the proposed discovery scheme 1000 times in different UE dropenvironments.

Referring to FIG. 37, in the case of the three schemes, the almost samenumber of UEs successfully access the infrastructure, and here, in thecase of scheme 2 in which the number of discovered UEs is larger thanthose of other schemes as illustrated in FIG. 35, since the number ofterminals accessing the infrastructure is almost the same, while thenumber of discovered UEs is greater than those of the other two schemes,the infrastructure access probability is slightly low.

To sum up, in the present invention, the D2D UE discovery scheme basedon response delay is proposed as a solution to the problem that resourceconflict inevitably occurs due to indiscriminate signal transmissionsduring a process in which UEs of a disaster area which have received adiscovery signal detect the discovery signal and transmit a responsesignal so resource is ineffectively used.

It is confirmed that, when a UE for transmitting a discovery signal isselected from UEs of a disaster area, three terminal selection methodsare considered, and average performances in terms of network coverageand network access are compared. When a UE which transmits a responsesignal the latest is selected and perform discovery, the number ofdiscovered UEs is the largest, obtaining better network coverageperformance than two other schemes, and the average numbers of UEssuccessfully accessing a network are similar in performance in the threecases.

Device to Which Present Invention is Applicable

FIG. 38 is a view illustrating a block diagram of a wirelesscommunication device according to an embodiment of the presentinvention.

Referring to FIG. 38, a wireless communication system includes a basestation (BS) (or eNB) 3810 and a plurality of terminals (or UEs) 3820positioned within coverage of the BS 3810.

The eNB 3810 includes a processor 3811, a memory 3812, and a radiofrequency (RF) unit 3813. The processor 3811 implements functions,processes and/or methods proposed in FIGS. 1 through 37. Layers of radiointerface protocols may be implemented by the processor 3811. The memory3812 may be connected to the processor 3811 to store various types ofinformation for driving the processor 3811. The RF unit 3813 may beconnected to the processor 3811 to transmit and/or receive a wirelesssignal.

The UE 3820 includes a processor 3821, a memory 3822, and a radiofrequency (RF) unit 3823. The processor 3821 implements functions,processes and/or methods proposed in FIGS. 1 through 37. Layers of radiointerface protocols may be implemented by the processor 3821. The memory3822 may be connected to the processor 3821 to store various types ofinformation for driving the processor 3821. The RF unit 3823 may beconnected to the processor 3821 to transmit and/or receive a wirelesssignal.

The memory 3812 or 3822 may be present within or outside of theprocessor 3811 or 3821 and may be connected to the processor 3811 or3821 through various well known units. Also, the eNB 3810 and/or the UE3820 may have a single antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined mannerEach of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

An embodiment of the present invention may be implemented by variousmeans, for example, hardware, firmware, software or a combination ofthem. In the case of implementations by hardware, an embodiment of thepresent invention may be implemented using one or moreApplication-Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers and/ormicroprocessors.

In the case of implementations by firmware or software, an embodiment ofthe present invention may be implemented in the form of a module,procedure, or function for performing the aforementioned functions oroperations. Software code may be stored in the memory and driven by theprocessor. The memory may be placed inside or outside the processor, andmay exchange data with the processor through a variety of known means.

It is evident to those skilled in the art that the present invention maybe materialized in other specific forms without departing from theessential characteristics of the present invention. Accordingly, thedetailed description should not be construed as being limitative fromall aspects, but should be construed as being illustrative. The scope ofthe present invention should be determined by reasonable analysis of theattached claims, and all changes within the equivalent range of thepresent invention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

In the wireless communication system of this disclosure, an example of aterminal discovery method in D2D communication applied to a 3GPPLTE/LTE-A system is described, but the terminal discovery method mayalso be applied to various wireless communication systems other than the3GPP LTE/LTE-A system.

The invention claimed is:
 1. A method for discovering a differentterminal in a wireless communication system supporting device-to-device(D2D) communication, the method comprising: transmitting, by a terminal,a discovery signal for detecting neighboring terminals for the D2Dcommunication; receiving, by the terminal, a response signal as aresponse with respect to the discovery signal from the differentterminal, wherein the response signal is transmitted by the differentterminal when a response delay time determined on the basis of areception signal-to-interference noise ratio (SINR) terminates;detecting the different terminal based on the received response signal;selecting, by the terminal, a specific terminal for performing aterminal discovery process at a next discovery period, from amongterminals which have transmitted the response signal; and transmitting,by the terminal, information of a resource pool for transmission of adiscovery message by the selected specific terminal at the nextdiscovery period to the selected specific terminal.
 2. The method ofclaim 1, wherein the response delay time is determined to be in inverseproportion to the reception SINR.
 3. The method of claim 1, wherein thespecific terminal for performing the terminal discovery process at thenext discovery period is selected as a terminal which has firsttransmitted the response signal.
 4. The method of claim 1, wherein thespecific terminal for performing the terminal discovery process at thenext discovery period is selected as a terminal which has transmittedthe response signal the latest.
 5. The method of claim 1, wherein thespecific terminal for performing the terminal discovery process at thenext discovery period is selected randomly.
 6. The method of claim 1,wherein the discovery signal includes a terminal identifier and/ordiscovery period information.
 7. The method of claim 1, furthercomprising: after transmitting the discovery signal, switching theterminal to a reception mode.
 8. The method of claim 1, wherein theterminal transmits the discovery signal only once during a discoveryperiod and maintains a reception mode to receive a response signaltransmitted from the neighboring terminals for a remaining time of thediscovery period.
 9. The method of claim 1, wherein the specificterminal is a terminal having a shortest response delay time or alongest response delay time.
 10. A method for discovering a terminal ina wireless communication system supporting device-to-device (D2D)communication, the method comprising: receiving, by the terminal, adiscovery signal for detecting neighboring terminals for the D2Dcommunication from a neighboring terminal; determining, by the terminal,a response delay time on the basis of a reception signal-to-interferencenoise ratio (SINR); transmitting, by the terminal, a response signal asa response with respect to the discovery signal when the response delaytime terminates, wherein the terminal is detected by the neighboringterminal based on the response signal; and receiving information of aresource pool for transmitting, by the terminal, a discovery message ata next discovery period from the neighboring terminal, if the terminalis selected by the neighboring terminal to perform a terminal discoveryprocess at the next discovery period.
 11. The method of claim 10,wherein the response delay time is determined to be in inverseproportion to the reception SINR.
 12. The method of claim 10, whereinthe reception SINR is derived on the basis of the discovery signal or areference signal transmitted from the terminal which has transmitted thediscovery signal.